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Expanding automotive electronic systems

1. ZTV A 2 IZVL n 0ZV L I 61VL SS BIVL LIVL O I i 9IVL 1 Me SIVL 5 SS i vIVL N z EIVL ZIVL j E OIVL SS u 6VL I Se a i SVL T 9V1 J 2 SVL 3 E CNL a SP ya pal 5 INN i Fr graat HOSV EE 002 NR E A g xipueddy 022 pi d u u iy t aber lasprurrcials ZQ Sma a fer fren pe ference coerced Ga Fer los TE GPIB Tutorial In 1965 Hewlett Packard designed the Hewlett Packard Interface Bus HP IB to connect their line of programmable instru ments to their computers Because of its high transfer rates nominally 1 Mbytes s this interface bus quickly gained popularity It was later accepted as IEEE Standard 488 1975 and has evolved to ANSI IEEE Standard 488 1 1987 Today the name General Purpose Interface Bus GPIB is more widely used than HP IB ANSI IEEE 488 2 1987 strengthened the original standard by defining precisely how controllers and instruments communicate Standard Commands for Programmable Instruments SCPI took the command structures defined in IEEE 488 2 Figure 1 GPIB History and created a single comprehensive programming command set that is used 1965 1975 1987 1990 1992 1993 with any SCPI instrument Figure 1 e Interface messages manage the bus Usually Talkers Listeners and summarizes GPIB history called commands or command messages Controllers interface messages perform such f
2. 1 5K 5 15K 5 15K 5 Figure 2 Full Speed Device with pull up resistor connected to D left Low Speed Device with pull up resistor connected to D right On low and full speed devices a differential 1 is transmitted by pulling D over 2 8V with a 15K ohm resistor pulled to ground and D under 0 3V with a 1 5K ohm resistor pulled to 3 6V see Fig 2 A differential 0 on the other hand is a D greater than 2 8V and a D less than 0 3V with the same appropriate pull down up resistors The receiver defines a differential 1 as D 200mV greater than D and a differential 0 as D 200mV less than D The polarity of the signal is inverted depending on the speed of the bus Therefore the terms J and K states are used in signifying the logic levels In low speed a J state is a differential 0 In high speed a J state is a differential 1 USB transceivers will have both differential and single ended outputs Certain bus states are indicated by single ended signals on D D or both For example a single ended zero or SEO can be used to signify a device reset if held for more than 10mS A SEO is generated by holding both D and D low lt 0 3V Single ended and differential outputs are important to note if you are using a transceiver and FPGA as your USB device You cannot get away with sampling just the differential output The low speed full speed bus has a characteristic impedance of
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4. IEEE 488 2 defined a number of require ments for a Controller including an exact set of IEEE 488 1 interface capabilities such as pulsing the interface clear line for 100 ps setting and detecting EOI setting asserting the REN line sensing the state and transition of the SRQ line sensing the state of NDAC and timing out on any I O transaction Other key Send ATN true commands Set address to send data Send ATN false data Send a program message Set address to receive data Receive ATN false data Receive a response message Pulse IFC line Place devices in DCAS Place devices in local state Place devices in remote state Place devices in remote with local lockout state Place devices in local lockout state Read IEEE 488 1 status byte Send group execution trigger GET message Give control to another device Conduct a parallel poll Configure devices parallel poll responses Disable devices parallel poll capability Control Sequence Compliance SEND COMMAND Mandatory SEND SETUP Mandatory SEND DATA BYTES Mandatory SEND Mandatory RECEIVE SETUP Mandatory RECEIVE RESPONSE MESSAGE Mandatory RECEIVE Mandatory SEND IFC Mandatory DEVICE CLEAR Mandatory ENABLE LOCAL CONTROLS Mandatory ENABLE REMOTE Mandatory SET RWLS Mandatory SEND LLO Mandatory READ STATUS BYTE Mandatory TRIGGER Mandatory PASS CONTROL Optional PERFORM PARALLEL POLL Optional PARALLEL POLL CONFI
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6. Endpoint Endpoint Descriptor Descriptor Endpoint Descriptor Endpoint Endpoint Descriptor Endpoint Endpoint Descriptor Endpoint Descriptor Descriptor Descriptor The interface descriptor could be seen as a header or grouping of the endpoints into a functional eroup performing a single feature of the device For example you could have a multi function fax scanner printer device Interface descriptor one could describe the endpoints of the fax function Interface descriptor two the scanner function and Interface descriptor three the printer function Unlike the configuration descriptor there is no limitation as to having only one interface enabled at a time A device could have one or many interface descriptors enabled at once Interface descriptors have a bInterfaceNumber field specifying the Interface number and a bAlternateSetting which allows an interface to change settings on the fly For example we could have a device with two interfaces interface one and interface two Interface one has bInterfaceNumber set to zero indicating it is the first interface descriptor and a bAlternativeSetting of zero Interface two would have a bInterfaceNumber set to one indicating it is the second interface and a bAlternativeSetting of zero default We could then throw in another descriptor also with a bInterfaceNumber set to one indicating it is the second interface but this time setting the bAlternativeSetting to one indic
7. Local Eu 4 Lal Bus Z Local Byss ME hka Fe H E JE K nn 5 z ER Malbus Multisystem Extension Interface Bus 22 bit Muliplesd Address and Dep Pathes v t Denn S bit 4 dress oder for hipe Address Spaces Singe Leva Hulti baser Poontzed Bus Arbitration Imeruptos pa bil rb with Single Shared Lire Bus Error Capabilty tor Desdock Resoluon and Remote Bue Error Ferd Figure 7 MXIbus Hardware Memory Mapped Communication 12 MXIbus Signals MXTIbus signals include 32 multiplexed address and data lines with parity address modifiers for multiple address spaces single level multimaster prioritized bus arbitration a single interrupt line a bus error line for handling timeouts and deadlock conditions and handshake lines for asynchronous operation Data transfers of 8 16 and 32 bits are possible as well as invisible read write operations and integrated block mode transfers With synchronous MXI the MXI 2 product line can achieve burst data rates as high as 33 Mbytes s and sustained throughput rates exceeding 20 Mbytes s regardless of the length of the MXI 2 cable MXIbus Cables A single MXI cable can be any length up to 20 m Up to eight MXI devices can be daisy chained on a single MXI cable length If multiple MXI devices are daisy chained together the total cable distance must be no more than 20 m The MXI 1 cable is a flexible round cable similar to a GPIB cable about 0 6 in in diameter Internally there are 48 singl
8. All devices should be powered on All devices should use 48 mA three state drivers Device capacitance on each GPIB signal should be less than 50 pF per device Bus extenders and an expander are available from National Instruments when your system exceeds these limits IEEE 488 2 and SCPI The SCPI and IEEE 488 2 standards addressed the limitations and ambiguities of the original IEEE 488 standard IEEE 488 2 makes it possible to design more compatible and productive test systems SCPI simplifies the programming task by defining a single comprehensive command set for programmable instru mentation regardless of type or manufacturer The scope of each of the IEEE 488 IEEE 488 2 and SCPI standards is shown in Figure 6 The ANSI IEEE Standard 488 1975 now called IEEE 488 1 greatly simplified the interconnection of programmable instrumentation by clearly defining mechanical electrical and hardware protocol specifications For the first time instruments from different manufacturers were interconnected by a standard cable Although this standard went a long way towards improving the productivity of test engineers the standard did have a number of shortcomings Specifically IEEE 488 1 did not address data formats status reporting message exchange protocol common configuration commands or device specific commands As a result each SAS ge GPIB Tutorial manufacturer implemented these items differently leaving
9. mmaa Passive safety reduced personal injury in event of an accident Underfloor concept ag Automatic Active safety avoiding an accident Side air bag Side impact protection qe Se Active seat belts BN 4 Air bag E Deformation e elements 4 4 Compound glass fw 4 Pes Seat belt 4 4 4 Safety cell Ps BS Safety potential us 1960 1970 1980 1990 2000 Active body control Antilock brake system Adaptive cruise control Brake assist system Brake by wire Collision avoidance Drive by wire Electromechanical brakes Electromechanical steering Electronic stability program Electronic traction control Steer by wire with mechanical backup Figure 3 Past and 2 kW If historical trends continue internal power future active and d emand will grow at a rate of 4 percent a year passive safety sys C I onservative estimates put the average electrical tems Advanced power requirements for high end vehicles at 2 5 kW electronic systems b 7 y 2005 These increases place strains on conven and the X by wire I i tional power equipment For example at a 3 kW infrastructure will i load bracket mounted belt driven alternators gen enable active safety W sz I i erate unpleasant noises and require liquid cooling improvements Table 1 shows some anticipated electrical loads for key emerging systems Analysts expect the loads to reach the
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12. exponential increase in the number and sophistication of electronic systems in vehi cles Today the cost of electronics in lux ury vehicles can amount to more than 23 percent of the total manufacturing cost Analysts estimate that more than 80 percent of all automo tive innovation now stems from electronics To gain an appreciation of the sea change in the average dollar amount of electronic systems and silicon components such as transistors microprocessors and diodes in motor vehicles we need only note that in 1977 the average amount was 110 while in 2001 it had increased to 1 800 The growth of electronic systems has had impli cations for vehicle engineering For example today s high end vehicles may have more than 4 kilometers of wiring compared to 45 meters in vehicles man ufactured in 1955 In July 1969 Apollo 11 employed a little more than 150 Kbytes of onboard memory to go to the moon and back Just 30 years later a family car might use 500 Kbytes to keep the CD player from skipping tracks The resulting demands on power and design have led to innovations in electronic networks for auto mobiles Researchers have focused on developing electronic systems that safely and efficiently replace entire mechanical and hydraulic applications and increasing power demands have prompted the development of 42 V automotive systems IN VEHICLE NETWORKS Just as LANs connect computers control net works connect a v
13. Current progress on the SP50 is as follows Physical Completed Specification includes 31 25 kbit sec 1 Mbit sec and 2 5 Mbit sec data transfer rates Requirements for fieldbus component parts Media and network configuration requirements for data integrity and interoperability between devices Fr n http www kvaser se can general htm The CAN bus The CAN bus is a broadcast type of bus This means that all nodes can hear all transmissions There is no way to send a message to just a specific node all nodes will invariably pick up all traffic The CAN hardware however provides local filtering so that each node may react only on the interesting messages The bus uses two different signaling states dominant logically 0 and recessive logically 1 These correspond to certain electrical levels which depend on the physical layer used there are several The modules are connected to the bus in a wired and fashion if just one node is driving the bus to the dominant state then the whole bus is in that state regardless of the number of nodes transmitting a recessive state In order to eliminate the DC component on the bus the CAN messages are bit stuffed that is for every occurrence of five consecutive bits of the same level the transmitter inserts an extra bit of the opposite level The receiver removes these extra bits The CAN messages CAN uses short messages the maximum utility load is 94 bits There is no explicit addres
14. Fieldbus Organisations This section establishes who have been the major instigators of fieldbus development over the past several years A brief summary of the developing standard is also covered The major players in the fieldbus area were previously dominated by two major groups e WorldFIP World Factory Instrumentation Protocol e ISP Interoperable Systems Project However recently these two groups have joined together to form the Fieldbus Foundation FF The Fieldbus Foundation and another organisation known as Profibus ISP are now competing for market dominance Two standards bodies known as the IEC International Electrotechnical Commission and the ISA Industry Society of America are currently working on an international standard known as SP50 This standard will hopefully allow the manufacturers of fieldbus equipment all around the world to produce compatible instruments for industrial applications WorldFIP ISP and FF have pledged that they will eventually evolve their products to meet the standard when it arrives However when the standard finally does arrive users of existing non conforming equipment will run the risk of having obsolete equipment or having to purchase new systems at an excessive cost At the time of writing information regarding actual market share for the Fieldbus Foundation and Profibus ISP was not available but Process Engineering s Instrumentation Supplement for 1994 predicts that the Fieldbus Fo
15. and by the Talker when enabling the HS488 protocol e NDAC not data accepted Indicates when a device has or has not accepted a message byte The line is driven by all devices when receiving commands and by Listeners when receiving data messages Device C Figure 4 Linear Configuration e DAV data valid Tells when the signals on the data lines are stable valid and can be accepted safely by devices The Controller drives DAV when sending commands and the Talker drives DAV when sending data messages interface Management Lines Five lines manage the flow of information across the interface e ATN attention The Controller drives ATN true when it uses the data lines to send commands and drives ATN false when a Talker can send data messages e IFC interface clear The System Controller drives the IFC line to initialize the bus and become CIC e REN remote enable The System Controller drives the REN line which is used to place devices in remote or local program mode e SRQ service request Any device can drive the SRQ line to asynchronously request service from the Controller e EOI end or identify The EOI line has two purposes The Talker uses the EOI line to mark the end of a message string and the Controller uses the EOI line to tell devices to identify their response in a parallel poll Physical and Electrical Characteristics Devices are usually connected with
16. engineers set up the older mechanical systems at a single fixed operating point for the vehicle s life time X by wire systems in contrast feature dynamic interaction among system elements Replacing rigid mechanical components with dynamically configurable electronic elements trig gers an almost organic systemwide level of inte gration As a result the cost of advanced systems should plummet Sophisticated features such as chassis control and smart sensors now confined to luxury vehicles will likely become mainstream Figure 2 shows how dynamic driving control sys tems have been steadily adopted since the 1920s with more on the way Highly reliable and fault tolerant electronic con trol systems X by wire systems do not depend on conventional mechanical or hydraulic mechanisms They make vehicles lighter cheaper safer and more CO eb O ab E ke ABS TCS ABS EBD ESP ACC EHB EMB Increased dependency on electronics fuel efficient These self diagnosing and configurable systems adapt easily to different vehicle platforms and produce no environmentally harmful fluids Such systems can eliminate belt drives hydraulic brakes pumps and even steering columns Indeed by 2010 one in three new cars will fea ture electronic steering X by wire steering systems under development will replace the steering column shaft with angle sensors and feedback motors A wire network wi
17. s network architecture show ing the trend toward incorporating ever more extensive elec tronics January 2002 Media oriented systems transport The appli cations of MOST a fiber optic network pro Today s vehicle tocol with capacity for high volume stream networks are ing include automotive multimedia and per transforming sonal computer networking More than 50 automotive firms including Audi BMW Daimler components into Chrysler Becker Automotive and Oasis EAR SiliconSystems developed the protocol under truly distributed the MOST Cooperative http www mostnet electronic systems de main index html Time triggered protocol Designed for real time distributed systems that are hard and fault tolerant the time triggered protocol ensures that there is no single point of failure The protocol has been proposed for systems that replace mechanical and hydraulic braking and steering sub systems TTP is an offshoot of the European Union s Brite Euram X by wire project Local interconnect network A master slave time triggered protocol the local interconnect network is used in on off devices such as car seats door locks sunroofs rain sensors and door mirrors As a low speed single wire enhanced ISO 9141 stan dard network LIN is meant to link to relatively higher speed networks like CAN LIN calms fears about security of serial networks in cars Because LIN provides a master slave protocol a would be th
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20. 2 Mandatory Common Commands S ui o _2 553 PE e EES oe U ij r O O E y c e Oe SOU BE s E a Sess Ss S E RS o E o ono O x O 3 2 amp gt O OG GC O Standard 6 5 4 3 2 1 0 Event Status Register ESR Logical OR pHi 11 1 E pias Lien Let e L Queue ze Se Ja Standard 1765 4321 Of Event Status Enable Output Queue Register ESE lt NRf gt ESE i loo EE J E Service ROS Y y lt Read by Serial Poll en 7 6 SEI Status Byte Register lt Read by STB SS ETT i SERE EA 8 D L Service Request 7 k Enable Register 8 SRE lt NRf gt i SRE gt 751431210 Do H Tas Figure 9 IEEE 488 2 Status Report Model ne A AN mr ld ew 4 AMA rr IAN PAL QA11 lafaldnatiner COM e www natinst com e Perhaps the two most important protocols are FINDLSTN and FINDRQS The FINDLSTN protocol takes advantage of the IEEE 488 2 Controller capability of monitoring bus lines to locate listening devices on the bus The Controller implements the FINDLSTN protocol by issuing a particular listen address and then monitoring the NDAC handshake line to determine if a device exists at that address The result of the FINDLSTN protocol is a list of addresses for all the located devices FINDLSTN is used at the start of an application program to ensure proper system con
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22. 9 9 Institute of the Motor Industry Volting Ahead on Power Systems http www just auto com features _detail asp art 307 current Dec 2001 Gabriel Leen is a technical researcher at PEI Tech nologies University of Limerick Ireland His research interests include in vehicle networks for mal verification of vehicle network protocols and automotive computing Leen has several years experience in automotive electronic system design He received a research MEng from the University of Limerick and is currently completing a PhD in automotive networking design Leen is a member of the Institution of Engineers of Ireland Contact him at gabriel leen ul ie Donal Heffernan is a lecturer in computer engi neering at the University of Limerick Ireland His research interests are real time embedded system design and reliable protocols for distributed control networks He received an MS in electrical engi neering from the University of Salford UK Hef fernan is a member of the Institution of Engineers of Ireland Contact him at donal heffernan ul ie Average load 800 300 300 100 200 60 360 100 2 220 January 2002
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28. Mbps the electromag netic radiation on twisted pair cables that results from a CAN s high speed operation makes pro viding electromagnetic shielding in excess of 500 Kbps too expensive CAN is a robust cost effective general control network but certain niche applications demand more specialized control networks For example X by wire systems use electronics rather than mechanical or hydraulic means to control a system These systems require highly reliable networks Emerging automotive networks X by wire solutions form part of a much bigger trend an ongoing revolution in vehicle electronics architecture Multimedia devices in automobiles such as DVD players CD players and digital TV sets demand networks with extensive synchronous bandwidth Other applications require wireless net works or other configurations To accommodate the broad and growing spectrum of vehicle network Mirror Self en I Light 1 ll Mirror MOST Speaker EE Window lift mm Universal light a M Lock M M E I Interior lig nt atas esas peeing heating Trunk M DI Heating M M NN H r II A Heating Universal motor Lock Semer Universal panel Global System for Mobile Communications applications research engineers are developing many specialized network protocols including the following Domestic Data Bus Matsushita and Philips jointly developed the Domestic Data Bus D2B standard m
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31. PXI also preserves investments in stand alone instruments or VXI systems by providing standard hardware and software for communication to these systems For example interfacing a PXI system to GPIB based instrumentation is no different with a PXI GPIB module than it is with a PCI GPIB module The software is identical Additionally a number of methods are available for interfacing PXI and Val together For more information refer to the Web Event on Hybrid PXI and VXI Systems Software Architecture Because PXI hardware is based on standard PC technologies such as the PCI bus as well as standard CPUs and peripherals the standard Windows software architecture is familiar to users as well Development and operation of Windows based PXI systems is no different from that of a standard Windows based PC Additionally because the PXI backplane uses the industry standard PCI bus writing software to communicate with PXI devices is in most cases identical to that of PCI devices For example software to communicate to an NI PXI 6251 multifunction data acquisition module is identical to that of an NI PCI 6251 board in aPC Therefore existing application software example code and programming techniques do not have to be rewritten or reused when moving software between PC based and PXI based systems As an alternative to Windows based systems you can use a real time software architecture for time critical applications requiring deterministic loop ra
32. SENSE subsystem is shown below to illustrate the tree system SENSe VOLTage DC RANGe lt range gt MINimum MAXimum VOLTage DC RANGe MINimum MAXimum FREQuency VOLTage RANGe lt range gt MINimum MAXimum FREQuency VOLTage RANGe MINimum MAXimum DETector BANDwidth 3 20 200 MINimum MAXimum DETector BANDwidth MINimum MAXimum ZERO AUTO OFF ONCE ON ZERO AUTO SENSe is the root keyword of the command VOLTage and FREQuency are second level keywords and Dc and VOLTage are third level keywords A colon separates a command keyword from a lower level keyword 154 Chapter 4 Remote Interface Reference An Introduction to the SCPI Language Command Format Used in This Manual The format used to show commands in this manual is shown below VOLTage DC RANGe lt range gt MINimum MAXimum The command syntax shows most commands and some parameters as a mixture of upper and lower case letters The upper case letters indicate the abbreviated spelling for the command For shorter program lines send the abbreviated form For better program readability send the long form For example in the above syntax statement VOLT and VOLTAGE are both acceptable forms You can use upper or lower case letters Therefore VOLTAGE volt and Volt are all acceptable Other forms such as VOL and VOLTAG will generate an error Braces enclose the parameter choices for a given command string
33. The braces are not sent with the command string A vertical bar separates multiple parameter choices for a given command string Triangle brackets lt gt indicate that you must specify a value for the enclosed parameter For example the above syntax statement shows the range parameter enclosed in triangle brackets The brackets are not sent with the command string You must specify a value for the parameter such as VOLT DC RANG 10 Some parameters are enclosed in square brackets 1 The brackets indicate that the parameter is optional and can be omitted The brackets are not sent with the command string If you do not specify a value for an optional parameter the multimeter chooses a default value 155 Chapter 4 Remote Interface Reference An Introduction to the SCPI Language Command Separators A colon is used to separate a command keyword from a lower level keyword You must insert a blank space to separate a parameter from a command keyword If a command requires more than one parameter you must separate adjacent parameters using a comma as shown below CONF VOLT DC 10 0 003 A semicolon is used to separate commands within the same subsystem and can also minimize typing For example sending the following command string TRIG DELAY 1 COUNT 10 18 the same as sending the following two commands TRIG DELAY 1 TRIG COUNT 10 Use a colon and a semicolon to link commands from
34. They do not require I O memory space or individual IRQ lines thus preventing IRQ conflicts when connecting external devices such as scanners or modems a problem common to old computers USB also allows for automatic device configuration and hot plug capability The hot plug or hot swap function means that you don t have to power down the computer and go through a restart when you want to connect a new device In instead you simply connect or disconnect the USB cable The computer will recognize the device and connect to the proper driver if installed Commonly installation of drivers for external hard drives printers scanners card readers are usually necessary while mice and keyboards that connect to the USB ports do not need specific drivers to be installed One of the benefits of USB is also bus powered devices devices which obtain its power from the bus and requires no external plug packs or additional cables The first USB standard was developed in the beginning of the nineties commonly referred to as USB 1 0 or USB 1 1 By 2001 it was superseded by a standard that allowed for a much higher data transfer rate USB 1 supported two speeds a full speed mode of 12Mbits s and a low speed mode of 1 5Mbits s The 1 5Mbits s mode is slower and less susceptible to EMI thus reducing the cost of ferrite beads and quality components For example crystals can be replaced by cheaper resonators USB 2 0 allows a transfer rate of up to 480Mbits s k
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36. Ways to Control a VXI System System configuration is divided into three categories The first type of VXI system consists of a VXI mainframe linked to an external controller via the GPIB The controller talks across the GPIB to a GPIB VXI interface module installed inside the VXI mainframe The GPIB VXI interface transparently translates the GPIB protocol to and from the VXI Word Serial protocol The second configuration involves a VXI based embedded computer The embedded computer is a VXI module that resides inside the VXI mainframe and connects directly to the VXI backplane This configuration offers the smallest physical size for a VXI system as well as performance benefits due to direct connection to the VXI backplane The third configuration uses a high speed MXIbus link from an external computer to control the VXI backplane The external computer operates as though it is embedded directly inside the VXI mainframe This configuration is functionally equivalent to the embedded method except that it has the flexibility for use with a wide variety of computers and workstations VXI Bus Interface Software One of the most important considerations when selecting a VXI system is software Software is the key to developing successful systems based on the VXIbus There are many programming languages operating systems and application development environments ADE to choose from when building a VXI system It is important to make the right decisions
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38. a shielded 24 conductor cable with both a plug and receptacle connector at each end see Figure 3 You can link devices in either a linear configuration see Figure 4 a star configuration see Figure 5 page 4 13 or a combination of the two The standard connector is the Amphenol or Cinch Series 57 MICRORIBBON or AMP CHAMP type For special interconnect applications an adapter cable with non standard cable and or connectors is used The GPIB uses negative logic with standard TTL levels When DAV is true for example it is a TTL low level lt 0 8 V and when DAV is false it is a TTL high level 2 2 0 V PHONE 512 794 0100 e Fax 512 794 8411 e info natinst com e www natinst com d Figure 5 Star Configuration Configuration Requirements To achieve the high data transfer rate for which the GPIB was designed the physical distance between devices and the number of devices on the bus are limited The following restrictions are typical for normal operation A maximum separation of 4 m between any two devices and an average separation of 2 m over the entire bus e A maximum total cable length of 20 m No more than 15 device loads connected to each bus with no less than two thirds powered on For higher speed systems using the 3 wire IEEE 488 1 handshake T1 delay 350 ns and HS488 systems the following restrictions apply e A maximum total cable length of 15 m with a device load per 1 m cable
39. a string parameter DISPlay TEXT lt quoted string gt Output Data Formats Output data will be in one of formats shown in the table below Type of Output Data Output Data Format Non reading queries lt 80 ASCII character string Single reading IEEE 488 SD DDDDDDDDESDD lt n gt Multiple readings IEEE 488 SD DDDDDDDDESDD lt nl gt Single reading RS 232 SD DDDDDDDDESDD lt cr gt lt nl gt Multiple readings RS 232 SD DDDDDDDDESDD lt cr gt lt nl gt Negative sign or positive sign Numeric digits E Exponent lt nl gt newline character lt cr gt carriage return character 159 2 VXI Application Note 030 NATIONAL INSTRUMENTS The Software os the Bodrum Short Tutorial on VXI MXI Ron Wolfe The purpose of this application note is to help you gain an understanding of VXI and MXI concepts This application note is divided into two tutorial sections The first section discusses V XI and the second section discusses MXI VXI Tutorial This section contains an overall introduction to VXI VMEbus eXtensions for Instrumentation What is VXI V XIbus is an exciting and fast growing platform for instrumentation systems The VXI Consortium was formed in 1987 with a charter of defining a multivendor instrument on a card standard Since that time the Consortium has defined system level components required for hardware interoperatibility The IEEE officially adopted the VXI spe
40. be easily integrated into these devices Just recently released has been the On The Go specification which adds peer to peer functionality to USB This introduces USB hosts into mobile phone and electronic organisers and thus has included a specification for mini A plugs mini A receptacles and mini AB receptacles Table I USB Pin Functions Standard internal wire colours are used in USB cables making it easier to identify wires from manufacturer to manufacturer The standard specifies various electrical parameters for the cables It is interesting to read the detail the original USB 1 0 spec included You would understand it specifying electrical attributes but paragraph 6 3 1 2 suggested the recommended colour for overmolds on USB cables should be frost white how boring USB 1 1 and USB 2 0 was relaxed to recommend Black Grey or Natural Electrical Unless you are designing the silicon for a USB device transceiver or USB host hub there is not all that much you need to know about the electrical specifications the essential points will be addressed here It uses four shielded wires of which two are power 5V and GND The remaining two are twisted pair differential data signals It uses a NRZI Non Return to Zero Invert encoding scheme to send data with a sync field to synchronise the host and receiver clocks and is bit stufted to ensure adequate transitions in the data stream Low Speed Device Full Speed Device
41. be the single most important consideration for the performance of your system Data Transfer Rates A common benchmark for VXI computers is the Block Data Rate This benchmark is easy for vendors to isolate and measure under ideal conditions It is important to understand what Block Data Rate means to your application Block Data Rate is the rate at which you can move a large block of data to or from memory on an ideal VXI device using back to back VXI transfers It does not measure how fast the computer can process the blocks of data or store them to disk once they are moved or whether your instruments themselves can actually match that data rate Most applications are not limited by the Block Data Rate of the VXI interface hardware but rather by the total time required to both move and handle the data or by the rate at which the instruments themselves can generate or accept the data Block Data Rate is easy for vendors to specify but often difficult for users to relate to overall system performance It is only one of many elements that affect the actual throughput of your system For example Block Data Rate does not indicate the processing power of your computer or the performance of the instruments themselves In addition a benchmark for Block Data Rate does not measure how fast you can control instruments using VXI Word Serial Protocol or random VXI reads and writes The speed for Word Serial communication and random VXI reads and writes 1s dep
42. built in hubs Up to 127 devices can be connected to any one USB bus at any one given time The loading of the appropriate driver when a device in plugged into the bus is done using a PID VID Product ID Vendor ID combination The VID is supplied by the USB Implementor s forum at a cost and this is seen as another sticking point for USB The latest info on fees can be found on the USB Implementor s Website Other standards organizations provide an extra VID for non commercial activities such as teaching research or fiddling The Hobbyist In these cases you may wish to use one assigned to your development system s manufacturer For example most chip manufacturers will have a VID PID combination you can use for your chips which is known not to exist as a commercial device Other chip manufacturers can even sell you a PID to use with their VID for your commercial device Another more notable feature of USB is its transfer modes USB supports Control Interrupt Bulk and Isochronous transfers While we will look at the other transfer modes later Isochronous allows a device to reserve a defined about of bandwidth with guaranteed latency This is ideal in Audio or Video applications where congestion may cause loss of data or frames to drop Each transfer mode provides the designer tradeoffs in areas such as error detection and recovery guaranteed latency and bandwidth Hardware Connectors All devices have an upstream connection to the host and al
43. listed levels by 2005 Electromechanical valves that will replace the camshaft and inlet and exhaust valves offer one exception they probably won t be produced until 2010 Given the benefits they offer such systems and their greater power loads are necessary Electro mechanical valves for example should provide a 15 percent improvement in fuel consumption Preheated catalytic converters will decrease exhaust emissions by 60 to 80 percent THE 42 V SOLUTION To meet the increasing demand for power a belt less engine with an integrated alternator starter on the flywheel operating at a 42 V potential offers the most promising proposed solution The motive for the new 42 V system is clear 79 percent of the Computer emergency call Smart adaptive controls Precrash sensn action Autonomous driving Collision avoidance Highway copilot Platooning EMB amp EMS Emergency brake SbW wb Environment recognition BbW wb Road recognition LDW JYUEISISSE JAA 2010 Electronic brakeforce distribution energy entering a conventional engine does not make it to the driveline The standard Lundell claw and rotor alternator is itself only 30 percent efficient at high speeds and 70 percent efficient at low speeds Thus generating a watt of electrical power requires about 2 watts of mechanical power with the lost watt turned into heat The integrated system is expected to be 20 per cent more efficient providi
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45. no defined USB format that is you can send any type of data down a stream pipe and can retrieve the data out the other end Data flows sequentially and has a pre defined direction either in or out Stream pipes will support bulk isochronous and interrupt transfer types Stream pipes can either be controlled by the host or device Message Pipes have a defined USB format They are host controlled which are initiated by a request sent from the host Data is then transferred in the desired direction dictated by the request Therefore message pipes allow data to flow in both directions but will only support control transfers Endpoint types The Universal Serial Bus specification defines four transfer endpoint types e Control Transfers Control transfers are typically used for command and status operations They are essential to set up a USB device with all enumeration functions being performed using control transfers They are typically bursty random packets which are initiated by the host and use best effort delivery The packet length of control transfers in low speed devices must be 8 bytes high speed devices allow a packet size of 8 16 32 or 64 bytes and full speed devices must have a packet size of 64 bytes e Interrupt Transfers Any one who has had experience of interrupt requests on microcontrollers will know that interrupts are device generated However under USB if a device requires the attention of the host it must wait until
46. node can be active i e it can transmit and receive extended frames or passive i e it will silently discard received extended frames e 1 x refers to the original specification and its revisions 2 0A and 1 x are compatible New CAN controllers today are usually of the 2 0B type A 1 x or 2 0A type controller will get very upset if it receives a message with 29 arbitration bits A 2 0B passive type controller will tolerate them a 2 0B active type controller can both transmit and receive them Controllers implementing 2 0B and 2 0A are compatible as long as the controllers implementing 2 0B refrain from sending extended frames Sometimes people advocate that standard CAN is better than Extended CAN because there are more overhead in the Extended CAN messages This is not necessarily true If you use the Arbitration Field for transmitting data then Extended CAN may actually have a lower overhead than has Standard CAN Basic CAN vs Full CAN The terms Basic CAN and Full CAN originate from the childhood of CAN Once upon a time there was the Intel 82526 CAN controller which provided a DPRAM style interface to the programmer Then come along Philips with the 82C200 which used a queue oriented programming model To distinguish between the two programming models people for some reason termed the Intel way as Full CAN and the Philips way as Basic CAN Today most CAN controllers allow for both programming models so there is no reason
47. of service and maintenance equipment will provide other obsta cles Still annual power consumption increases of 4 percent will simply overload present day 14 V systems making 42 V alternatives inevitable works will bring an explosion of new func tionality and innovation Our vehicles will become more like PCs creating the potential for a host of plug and play devices With over 50 million new vehicles a year this offers the potential for vast growth in automotive application software much like that of the PC industry over the past decade On average US commuters spend 9 percent of their day in an automobile Introducing multimedia and telematics to vehicles will increase productiv ity and provide entertainment for millions Further X by wire solutions will make computer diagnos tics a standard part of mechanics work The future could even bring the introduction of an electronic chauffeur H educing wiring mass through in vehicle net Acknowledgments We thank the Byteflight Group DaimlerChrysler Delphi Automotive the FlexRay Group Siemens Motorola PEI Technologies TTTech and the Uni versity Of Limerick for their assistance References 1 J M Miller et al Making the Case for a Next Gen eration Automotive Electrical System MIT Indus try Consortium on Advanced Automotive Electrical Electronic Components and Systems http auto mit edu consortium current Dec 2001 2 W Powers Environ
48. our industry By using general purpose computers the instrumentation industry directly benefits from the billions of R amp D dollars spent each year in the general computer market Most VXI users would prefer to use an industry standard computer provided by a computer vendor rather than a VXI specific computer provided by an instrument vendor In fact for VXI to truly become the platform for the next millennium it must align itself with the powerful general computer market Then VXI can take advantage of the billions of dollars being spent and bring this investment to bear on the needs of the instrumentation community VXI must be able to take full advantage of industry standard PCs with PCI EISA and ISA as well as workstations from Sun HP and others VXI also must have a transparent mechanism for extending to multiple mainframes and a way to accommodate instruments that cannot physically fit on a VXI module MXIbus meets each of these needs The Need for MXIbus Today s market demands that you add value to our Test amp Measurement systems You need modular testing systems that can evolve with technological innovations in our industry You want increased data throughput and the utmost in computing power you want flexible high speed connectivity between multiple VXI VME mainframes and you want to be able to keep up with innovations in PC and workstation technology Today sophisticated I O architectures such as PCI are accelerating data th
49. requirement to 1 2 in so that there is enough room for the module to be completely enclosed in a metal case for shielding The metal cases connect to backplane grounds Thus you can use existing VME boards in a VXIbus chassis but not vice versa The VXIbus specification also has conducted emissions and susceptibility requirements which prevent any power supply noise from affecting the performance of a module For far field radiated emissions such as FCC and VDE each module must not contribute more than its share of the total For example in a mainframe that holds 13 modules each module must not contribute more than 1 13 of the allowed total Because of the desire for extremely precise time coupling between modules using the backplane it is necessary to minimize the noise and crosstalk on the backplane clock and trigger signal lines The backplane is required to be a single monolithic board across any one slot The VXIbus specification has a tutorial section on how to design a backplane for low noise and high signal integrity Hardware Registers VXI modules must have a specific set of registers located at specific addresses as shown in Figure 3 The upper 16 KB of the 64 KB A16 address space are reserved for VXIbus devices Each VXI device has an 8 bit logical address that specifies where its registers are located in this address space A single VXI system can have up to 256 VXI devices The logical address of a VXI device which can be manuall
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52. the test system developer with a formidable task IEEE 488 2 enhanced and strengthened IEEE 488 1 by standardizing data formats status reporting error handling Controller functionality and common commands to which all instruments must respond in a defined manner By standardizing these issues IEEE 488 2 systems are much more compatible and reliable The IEEE 488 2 standard focuses mainly on the software protocol issues and thus maintains compatibility with the hardware oriented IEEE 488 1 standard SCPI built on the IEEE 488 2 standard and defined device specific commands that standardize programming instruments SCPI systems are much easier to program and maintain In many cases you can interchange or upgrade instruments without having to change the test program The combination of SCPI and IEEE 488 2 offers significant productivity gains and finally delivers as sound a software standard as IEEE 488 1 did a hardware standard IEEE 488 2 IEEE Standard 488 2 1987 encouraged a new level of growth and acceptance of the and Set Syntax and Data Str 488 2 488 1 488 2 Figure 6 Evolution of GPIB Instrumentation Standards PHONE 512 794 0100 e Fax 512 794 8411 e info natinst com e www natinst com NATIONAL INSTRUMENTS 4 13 i lt mis a GPIB Tutorial e IEEE 488 bus or GPIB by addressing problems that had arisen from the original IEEE 488 standard IEEE 488 2 was drafted on the pr
53. to realize all of the advantages that VXI has to offer while minimizing your development costs now and in the future Your software decisions not only affect overall system performance and system capability but also development time and productivity You should choose tools that have complete debugging capability and that work with the most popular operating systems and programming languages If you choose to program your VXI system using a standard language such as C C Basic ADA or ATLAS you should realize that standard programming languages do not come with built in VXI capability Rather VXI capability is added through a VXI bus interface software library This software component is very important because it affects the choice of VXI computer hardware operating system programming language and ADE Industry Wide Software Standards As a step toward industry wide software compatibility the VXIplug amp play alliance developed one specification for I O software the Virtual Instrument System Architecture or VISA The VISA specification VPP 4 1 defines a next generation I O software standard not only for VXI but also for GPIB and serial interfaces With the VISA standard endorsed by over 50 of the largest instrumentation companies in the industry including Tektronix Hewlett Packard and National Instruments VISA unifies the industry by facilitating the development of interoperable and reusable software components able to stand the t
54. to use the terms Full CAN and Basic CAN in fact these terms can cause confusion and should be avoided Of course a Full CAN controller can communicate with a Basic CAN controller and vice versa There are no compatibility problems Message Arbitration The message arbitration the process in which two or more CAN controllers agree on who is to use the bus is of great importance for the really available bandwidth for data transmission The message arbitration of the CAN protocol consists mainly of comparing bit for bit of the Arbitration Field Any CAN controller may start a transmission when it has detected an idle bus This may result in two or more controllers starting a message almost at the same time The conflict is resolved in the following way The transmitting nodes monitor the bus while they are sending If they detect a dominant level when they are sending a recessive level themselves they will immediately quit the arbitration process and become receivers instead The arbitration is performed over the whole Arbitration Field and when that field has been sent exactly one transmitter is left on the bus This node continues the transmission as if nothing had happened No time is lost in the arbitration process An important condition for this bit wise arbitration to succeed is that no two nodes may transmit the same Arbitration Field There is one exception to this rule if the message contains no data then any node may tr
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60. 88 transfer rates can reach 1 5 Mbytes s HS488 Controllers always use the standard IEEE 488 1 3 wire handshake to transfer GPIB commands bytes with Attention ATN asserted ATN DIO 1 8 Composite DAV NRFD NDAC The Talker uses this HS488 wink signal the momentary low going pulse on NRFD to tell the Listener that the Talker is capable of sending data using HS488 PLONE 512 794 0100 e FAX 512 794 8411 e info natinst com e www natinst com First byte transferred using normal handshake Lack of NRFD transition indicates that all Listeners are HS488 capable Figure 8 HS488 Handshake T11 T12 gt Second byte transferred using HS488 rin EIA E nn nn nn AAA tr Ahanaol AU fP3Y9C 1 4 rite lame fer Chapter 4 Remote Interface Reference An Introduction to the SCPI Language An Introduction to the SCPI Language SCPI Standard Commands for Programmable Instruments is an ASCII based instrument command language designed for test and measurement instruments Refer to Simplified Programming Overview starting on page 112 for an introduction to the basic techniques used to program the multimeter over the remote interface SCPI commands are based on a hierarchical structure also known as a tree system In this system associated commands are grouped together under a common node or root thus forming subsystems A portion of the
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62. 90 ohms 15 It is therefore important to observe the datasheet when selecting impedance matching series resistors for D and D Any good datasheet should specify these values and tolerances High Speed 480Mbits s mode uses a 17 78mA constant current for signalling to reduce noise Speed Identification A USB device must indicate its speed by pulling either the D or D line high to 3 3 volts A full speed device pictured below will use a pull up resistor attached to D to specify itself as a full speed device These pull up resistors at the device end will also be used by the host or hub to detect the presence of a device connected to its port Without a pull up resistor USB assumes there is nothing connected to the bus Some devices have this resistor built into its silicon which can be turned on and off under firmware control others require an external resistor For example Philips Semiconductor has a SoftConnect technology When first connected to the bus this allows the microcontroller to initialise the USB function device before it enables the pull up speed identification resistor indicating a device is attached to the bus If the pull up resistor was connected to Vbus then this would indicate a device has been connected to the bus as soon as the plug is inserted The host may then attempt to reset the device and ask for a descriptor when the microprocessor hasn t even started to initialise the usb function device Other vendors s
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65. DDL DDL allows an instrument added to the bus system to communicate to a master control what its functions and capabilities are Some of the major members of ISP include Siemens Germany The Rosemount Group Minnesota Fisher Controls Inc Texas Foxoboro Co Massachusetts ABB Co Sweden Yokogawa Electric Corporation Tokyo Fieldbus Foundation On a positive note ISP and WorldFIP North American division have been working together since late 1993 on a possible merger of their technology A single solution has been what industry has needed for a long time so in June of 1994 the Fieldbus Foundation FF was set up between ISP and WorldFIP NA However at least 1 to 2 years of delay is expected before a complete product can be produced Profibus ISP Effectively a breakaway group of the Profibus and ISP organisations this group effectively announced to the world that they will have their own fieldbus communications system ready in approximately June July 1994 Profibus ISP is derived from the Profibus and ISP products and hence has the features of both with some small additions At the time of writing little information on Profibus ISP and the Fieldbus Foundation was available IEC ISA SP50 The ISA TEC are developing a standard with the working name of SP50 The standard will follow the ISO OSI seven layer model for data communications with an additional eighth layer which focuses on the product interoperablility
66. Elektrisk M tteknik LTH Datorbaserade m tsystem 3 Bussystem Lund 06 09 06 INNEH LL 1 GPIB The General Purpose Instrumentation Bus GPIB Tutorial The SCPI language VXI PXI USB An introduction to USB Faltbussar What is Fieldbus The CANbus Electronics in cars AAA EE e e Ae ke ca te Zeeche AE RR AS CO TER aber Sad Je JO 19quinu Surmos3 e EPOWWOIIE o JIQIXI Y JESSIII 94 YM pousisap u q sey 1 ALY yuswd nba 3597 onewozne JO uOrejuawojdur pue u tsop y ur 1 uI8u 153 au JO 2101 oy sorzipduns Anea 1 mais te 398J19 U1 UL se pom se Audosomud USISIP L SI 31 99UIS NINY dy UT JO MOU UOHINPOIA ut 391Aap ea PUB YSIWON DI 9 10 oluonoo D1IJ09 9 Aue Jo Funsa ay aJeWO Ne pue Ji duuts o uoig3iunuutuo3 BM OM SMOJ YIYA 19 01JU09 10 13 ndwo2 e 0 SJUIWINIJSUL JJOL JO JUO JO u01e133 u1 ue praosd 0 paudisap NJaleo u q sey Wajs s 998J19JU1 QSp AAAI JUL IJWWPBIZOId 10 J9UBISIP LUIIS S ELIJO euoissajoid Y 0 99u3919 31 SgenjeA 9q SE A Se UBIDIUYIA JO Jasn WIIS S UUI 1S11J 34 0 93en3ue pue si opun o se3 ur USYLIM SJIeJ3p e91Uy9a n3 apiaoid jim 3 od sng uonejJuswngsuj asoding eJ9uan ay SB 0 P3119J31 JUOWIUIOO SI U3IUA Wajs s 998J19JU1 889 341 ay JO Sjeju wepuny y JO uondii5s p AJAJdWOI e SIPIAOIA yooq sty 1 NOLLDNAOALNI sng UONBJUJLUNIJSU asod ing P19095 JJ L Y z I tajdeyy PA UED LI
67. GURE Optional PARALLEL POLL UNCONFIGURE Optional Table 1 IEEE 488 2 Required and Optional Control Sequences RESET FINDRQS ALLSPOLL PASSCTL REQUESTCTL FINDLSTN SETADD TESTSYS Reset System Serial Poll All Devices Pass Control Request Control Find Listeners Set Address Self Test System Find Device Requesting Service Mandatory Optional Mandatory Optional Optional Optional Optional but requires FINDLSTN Optional Table 2 IEEE 488 2 Controller Protocols requirements for Controllers are bus control sequences and bus protocols IEEE 488 2 Control Sequences The IEEE 488 2 standard defined control sequences that specify the exact IEEE 488 1 messages that are sent from the Controller as well as the ordering of multiple messages IEEE 488 2 defined 15 required control sequences and four optional control sequences as shown in Table 1 The IEEE 488 2 control sequences describe the exact states of the GPIB and the ordering of command messages for each of the defined operations IEEE 488 2 control sequences remove the ambiguity of the possible bus conditions so instruments and Controllers are much more compatible By exactly defining the state of the bus and how devices should respond to specific messages IEEE 488 2 removes such system development problems PHONE 512 794 0100 e Fax 512 794 8411 e info natinst com e www natinst com IEEE 488 2 Protocols Protocols are high level routines
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69. Instruments PXI 8187 Pentium 4 M 2 5 GHz Embedded Controller Notice the familiar PC peripherals such as keyboard mouse and monitor connections as well as the hard drive USB 2 0 Ethernet serial and other standard PC peripherals This controller runs standard Windows 2000 XP OSs or can be targeted with LabVIEW Real Time Embedded controllers are ideal for portable systems and contained single box applications where the chassis is moved from one location to the next For more information please refer to PX controllers PXI Peripheral Modules National Instruments offers more than 100 different PXI modules and because PXI is an open industry standard nearly 1000 modules are available from the 65 members of the PXI Systems Alliance Analog Input and Output Protoyping Boards Boundary Scan Instruments Bus Interface amp Communication Motion Control Carrier Products Power Supplies al Receiver Interconnect Devices switching Timing Input and Output Digital Input and Output Digital Signal Processing Functional Test and Diagnostics Image Acquisition Because PXI is directly compatible with CompactPCl you can use any 3U CompactPCI module in a PXI system Additionally CardBus PCMCIA and PMC PCI Mezzanine Card cards can be installed in PXI systems using carrier modules For example the National Instruments PXI 8221 PC Card Carrier can be used to connect CardBus and PCMCIA devices to PXI systems
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76. SE Step 4 often confuses people writing firmware for the first time The Host asks for the first 64 bytes of the device descriptor so when the host resets your device after it receives the first 8 bytes it is only natural to think there is something wrong with your device descriptor or how your firmware handles the request However as many will tell you if you keep persisting by implementing the Set Address Command it will pay off by asking for a full 18 bytes of device descriptor next Normally when something is wrong with a descriptor or how it is being sent the host will attempt to read it three times with long pauses in between requests After the third attempt the host gives up reporting an error with your device 5 Faltbussar Fr n http www infoside de infida wissen_allgemein htm What is Fieldbus Fieldbus is a generic term which describes a new digital communications network which will be used in industry to replace the existing 4 20mA analogue signal The network is a digital bi directional multidrop serial bus communications network used to link isolated field devices such as controllers transducers actuators and sensors Each field device has low cost computing power installed in it making each device a smart device Each device will be able to execute simple functions on it s own such as diagnostic control and maintenance functions as well as providing bi directional communication capabilities With these dev
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80. The sync field is 8 bits long which is used to synchronise the clock of the receiver with the transmitter The last two bits indicate where the PID fields starts PID PID stands for Packet ID This field is used to identify the type of packet that is being sent The following table shows the possible values Packet Identifier Token a Handshake on Special oo RR There is 4 bits to the PID however to insure it is received correctly the 4 bits are complemented and repeated making an 8 bit PID in total The resulting format is shown below Pin Pi PD PID ne oio Pi PID e ADDR The address field specifies which device the packet is designated for Being 7 bits in length allows for 127 devices to be supported Address 0 is not valid as any device which is not yet assigned an address must respond to packets sent to address zero e ENDP The endpoint field is made up of 4 bits allowing 16 possible endpoints Low speed devices however can only have two endpoint additional addresses on top of the default pipe four endpoints max e CRC Cyclic Redundancy Checks are performed on the data within the packet payload All token packets have a 5 bit CRC while data packets have a 16 bit CRC e EOP End of packet Signalled by a Single Ended Zero SEO for approximately 2 bit times followed by a J for 1 bit time Common USB Packet Types USB has four different packet types Token packets i
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84. ansmit that message SInce the bus is wired and and a Dominant bit is logically 0 it follows that the message with the numerically lowest Arbitration Field will win the arbitration Error Handling Error handling is built into in the CAN protocol and is of great importance for the performance of a CAN system The error handling mainly aims at detecting errors in messages appearing on the CAN bus so that the Transmitter can retransmit an erroneous message Every CAN controller along a bus will try to detect errors within a message If an error is found the discovering node will transmit an Error Frame thus destroying the bus traffic The other nodes will detect the error caused by the Error Frame if they haven t already detected the original error and take appropriate action i e discard the current message Each node maintains two error counters the Transmit Error Counter and the Receive Error Counter There are several rules governing how these counters are incremented and or decremented In essence the a transmitter detecting a fault increments its Transmit Error Counter faster than the listening nodes will increment their Receive Error Counter This is because there is a good chance that it is the transmitter who is at fault When any Error Counter raises over a certain value the node will first become error passive that is it will not actively destroy the bus traffic when it detects an error and then bus off which means that the n
85. antee of bandwidth or minimum latency e Stream Pipe Unidirectional Full and high speed modes only Bulk transfers are only supported by full and high speed devices For full speed endpoints the maximum bulk packet size is either 8 16 32 or 64 bytes long For high speed endpoints the maximum packet size can be up to 512 bytes long If the data payload falls short of the maximum packet size it does not need to be padded with zeros A bulk transfer is considered complete when it has transferred the exact amount of data requested transferred a packet less than the maximum endpoint size of transferred a zero length packet USB Descriptors All USB devices have a hierarchy of descriptors which describe to the host information such as what the device is who makes it what version of USB it supports how many ways it can be configured the number of endpoints and their types etc The more common USB descriptors are e Device Descriptors e Configuration Descriptors e Interface Descriptors e Endpoint Descriptors String Descriptors USB devices can only have one device descriptor The device descriptor includes information such as what USB revision the device complies to the Product and Vendor IDs used to load the appropriate drivers and the number of possible configurations the device can have The number of configurations indicate how many configuration descriptors branches are to follow The configuration descriptor specifies values
86. at of commands sent to instruments and the format and coding of responses sent by instruments All instruments must perform certain operations to communicate on the bus and report status Because these operations are common to all instruments IEEE 488 2 defined the programming commands used to execute these operations and the queries used to receive common status information These common commands and queries are shown in Table 3 Because IEEE 488 2 standardizes status reporting the Controller knows exactly how to obtain status infor mation from every instrument in the system This status reporting model builds upon the IEEE 488 1 status byte to provide more detailed status information The status reporting model is shown in Figure 9 SCPI In April 1990 a group of instrument manufacturers announced the SCPI specification which defines a common command set for programming instruments Before SCPI each instrument manufacturer developed its own command sets for its programmable instruments This lack of standardization forced test system developers to learn a number of different command sets and instrument specific parameters for the various instruments used in an application leading to programming complexities and resulting in unpredictable schedule delays and development costs By defining a standard programming command set SCPI decreases development time and increases the readability of test programs and the ability to in
87. ating this interface descriptor can be an alternative setting to that of the other interface descriptor two When this configuration is enabled the first two interface descriptors with bAlternativeSettings equal to zero is used However during operation the host can send a SetInterface request directed to that of Interface one with an alternative setting of one to enable the other interface descriptor This gives an advantage over having two configurations in that we can be transmitting data over interface zero while we change the endpoint settings associated with interface one without effecting interface zero Each endpoint descriptor is used to specify the type of transfer direction polling interval and maximum packet size for each endpoint Endpoint zero the default control endpoint is always assumed to be a control endpoint and as such never has a descriptor String descriptors provide human readable information and are optional If they are not used any string index fields of descriptors must be set to zero indicating there is no string descriptor available Enumeration Enumeration is the process of determining what device has just been connected to the bus and what parameters it requires such as power consumption number and type of endpoint s class of product etc The host will then assign the device an address and enable a configuration allowing the device to transfer data on the bus A fairly generic enumeration process is detailed in
88. cification IEEE 1155 in March 1993 The VXIplug amp play Systems Alliance founded in September 1993 sought a higher level of system standardization to cover all VXI system components By focusing on software standardization the alliance defined standards to make VXI systems easy to integrate and use while maintaining multivendor software interoperatibility With the success of multivendor standards and solid technical specifications VXI is backed by more than 250 vendors with more than 1000 products available The success of VXI as an open multivendor platform is a testament to the value of multivendor standards and has made VXI the platform of choice for open instrumentation systems VXI is used in many different applications ranging from test and measurement and ATE to data acquisition and analysis in both research and industrial automation Although some VXI systems today are purely VXI many users are migrating to VXI by integrating it into existing systems consisting of GPIB instruments VME cards or plug in data acquisition DAQ boards You can control a VXI system with a remote general purpose computer using the high speed Multisystem eXtension Interface MXI bus interface or GPIB You can also embed a computer into a VXI chassis and control the system directly Whatever your system configuration needs may be VXI offers the flexibility and performance to take on today s most challenging applications The Need for VXIbus The demand f
89. dding commands for more specific or newer functionality is easily accommodated The SCPI Instrument Model As a means of achieving compatibility and categorizing command groups SCPI defined a model of a programmable instrument This model shown in Figure 10 applies to all the different types of instrumentation All of the functional components of the instrument model may not apply to every PHONE 512 794 0100 e FAX 512 794 8411 e info natinst com e www natinst com instrument For example an oscilloscope does not have the functionality defined by the signal generation block in the SCPI model SCPI defines hierarchical command sets to control specific functionality within each of these functional components The signal routing component controls the connection of a signal to the instruments internal functions the measurement component converts the signal into a preprocessed form and the signal generation component converts internal data to real world signals The memory component stores data inside the instrument The format component converts the instrument data to a form that you can transmit across a standard bus The trigger component synchronizes instrument actions with internal functions external events or other instruments The measurement function gives the highest level of compatibility berween instruments because a measurement is specified by signal parameters not instrument functionality In most case
90. different subsystems For example in the following command string an error is generated if you do not use both the colon and semicolon SAMP COUN 10 TRIG SOUR EXT Using the MIN and MAX Parameters You can substitute MINimum or MAXimum in place of a parameter for many commands For example consider the following command VOLTage DC RANGe lt range gt MINimum MAXimum Instead of selecting a specific voltage range you can substitute MIN to set the range to its minimum value or MAX to set the range to its maximum value 156 geng per Seet aution d Chapter 4 Remote Interface Reference An Introduction to the SCPI Language Querying Parameter Settings You can query the current value of most parameters by adding a question mark to the command For example the following command sets the sample count to 10 readings SAMP COUN 10 You can query the sample count by executing SAMP COUN You can also query the minimum or maximum count allowed as follows SAMP COUN MIN SAMP COUN MAX If you send two query commands without reading the response from the first and then attempt to read the second response you may receive some data from the first response followed by the complete second response To avoid this do not send a query command without reading the response When you cannot avoid this situation send a device clear before sending the second query command SCPI Command Terminator
91. e HS488 handshake shown in Figure 8 Once HS488 is enabled the Talker places a byte on the GPIB DIO lines f 4 WY omm mars e er First byte transferred Second byte Third byte Composite Some All Some ready ready All accepted accepted Figure 7 Normal IEEE 488 1 Handshake waits for a preprogrammed settling time asserts DAV waits for a preprogrammed hold time unasserts DAV and drives the next data byte on the DIO lines The Listener keeps NDAC unasserted and must accept the byte within the specified hold time A byte must transfer in the time set by the settling time and hold time without waiting for any signals to propagate along the GPIB cable HS488 Data Transfer Flow Control The Listener may assert NDAC to temporarily prevent more bytes from being transmitted or assert NRED to force the Talker to use the 3 wire handshake Through these methods the Listener can limit the average transfer rate However the Listener must have an input buffer that can accept short bursts of data at the maximum rate because by the time NDAC or NRFD propagates back to the Talker the Talker may have already sent another byte The required settling and hold times are user configurable depending on the total length of cable and number of devices in the system Between two devices and 2 m of cable HS488 can transfer data at up to 8 Mbytes s For a fully loaded system with 15 devices and 15 m of cable HS4
92. e ended twisted pair signal lines MXI 2 features an improved cabling scheme that uses a single double shielded cable between all devices and a single high density high reliability 144 pin connector per device In this fashion all MXI 2 devices share not only the MXTIbus itself but also the V XI defined trigger lines interrupt lines systems clocks and other signals that were available on MXI 1 products as an optional second connector and cable INTX MXI 1 products use an MXI 1 cable between devices and an optional INTX cable to share trigger timing information between mainframes in a multiple mainframe configuration MXI 2 eliminates the need for an additional INTX cable in your system Because of the cables differences you cannot mix MXI 1 and MXI 2 products in the same system Both MXI 1 and MXI 2 use double shielding with an aluminum mylar shield as well as a copper braid shield to eliminate any EMI problems and both cables meets the National Electric Code NEC CL2 fire safety code The stacking depth of two daisy chained MXI cables is approximately 3 3 in MXI is essentially a backplane bus in a cable Each MXI signal line is twisted with its own ground line All MXI signal lines are matched impedance to minimize signal skew and reflections Stub lengths no more than 4 in off the mainline interconnection minimize reflections due to impedance discontinuities Termination networks configured with onboard jumpers are located at the first and
93. e mid 1980s Bosch developed the controller area network one of the first and most enduring automotive control networks CAN is currently the most widely used vehicular network with more than 100 million CAN nodes sold in 2000 0018 9162 02 17 00 2002 IEEE Digital radio Vehicle computer Speaker Navigation Lock oa Seat E No H instruments d IS I S I l Central pela Additional systems Drive train poy contre s Roof ad Climate gt X66 OC gt Seat Steering wheel JEE anel M P Lock s MOST HITS CAN GPS GSM LIN Local interconnect network MOST Media oriented systems transport Controller area network Global Positioning System A typical vehicle can contain two or three sepa rate CANS operating at different transmission rates A low speed CAN running at less than 125 Kbps usually manages a car s comfort electronics like seat and window movement controls and other user interfaces Generally control applications that are not real time critical use this low speed network segment Low speed CANs have an energy saving sleep mode in which nodes stop their oscillators until a CAN message awakens them Sleep mode prevents the battery from running down when the ignition is turned off A higher speed CAN runs more real time criti cal functions such as engine management antilock brakes and cruise control Although capable of a maximum baud rate of 1
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95. e technologies and components Several protocols are suitable for X by wire appli cations TTP for example is a promising and avail able protocol geared toward improving driving safety However the FlexRay and TTCAN proto cols will start to compete with TTP when manu facturers look for more flexibility and lower cost Figure 3 shows the past and potential future improvements from active and passive safety sys tems such as air bags and road recognition sensors Advanced electronic systems and the X by wire infrastructure will enable most potential active safety improvements ELECTRICAL POWER DEMAND Vehicular battery management systems continu ously check the condition of the car s battery mon itoring the charge to ensure the auto will start and have enough power to maintain critical systems Even with the engine switched off some systems real time clocks keyless entry and security devices and vehicle control interfaces such as window switches and light switches still consume power In addition to these conventional electrical sys tems emerging applications as diverse as in car com puters and GPS navigation systems consume enough power to raise the total energy load to more than January 2002 Brake by wire Mechanical Figure 2 Past and projected progress in dynamic driving control systems As the cost of advanced systems plummets sophisticated fea tures are likely to become mainstream components
96. e triggered CAN has a session layer on top of the existing data link and physical lay ers The protocol implements a hybrid time trig gered TDMA schedule which also accommodates event triggered communications The ISO task force responsible for the development of TTCAN which includes many of the major automotive and semiconductor manufacturers developed the pro tocol TTCAN s intended uses include engine man agement systems and transmission and chassis controls with scope for X by wire applications Intelligent transportation systems data bus Enabling plug and play in off the shelf automotive electron ics the intelligent transportation systems data bus eliminates the need to redesign products for differ ent makes The Automotive Multimedia Interface Collaboration a worldwide organization of motor vehicle makers created the specification which sup ports high bandwidth devices such as digital radios digital videos car phones car PCs and navigation systems The specification s first release endorses IDB C CAN as a low speed network and optional audio bus and two high speed networks MOST and IDB 1394b IDB 1394b is based on the IEEE 1394 FireWire standard X BY WIRE SOLUTIONS Today s vehicle networks are not just collections of discrete point to point signal cables They are transforming automotive components once the domain of mechanical or hydraulic systems into truly distributed electronic systems Automotive
97. ehicle s electronic equipment These networks facilitate the sharing of informa Computer tion and resources among the distributed applica tions In the past wiring was the standard means of connecting one element to another As electronic content increased however the use of more and more discrete wiring hit a technological wall Added wiring increased vehicle weight weakened performance and made adherence to reliability standards difficult For an average well tuned vehi cle every extra 50 kilograms of wiring or extra 100 watts of power increases fuel consumption by 0 2 liters for each 100 kilometers traveled Also complex wiring harnesses took up large amounts of vehicle volume limiting expanded functionality Eventually the wiring harness became the single most expensive and complicated component in vehicle electrical systems Fortunately today s control and communications networks based on serial protocols counter the problems of large amounts of discrete wiring For example in a 1998 press release Motorola reported that replacing wiring harnesses with LANs in the four doors of a BMW reduced the weight by 15 kilo grams while enhancing functionality Beginning in the early 1980s centralized and then distributed net works have replaced point to point wiring Figure 1 shows the sheer number of systems and applications contained in a modern automobile s network architecture Controller area network In th
98. eing sent is not defined USB is made up of several layers of protocols While this sounds complicated don t give up now Once you understand what is going on you really only have to worry about the higher level layers In fact most USB controller I C s will take care of the lower layer thus making it almost invisible to the end designer Each USB transaction consists of a Token Packet Header defining what it expects to follow an Optional Data Packet Containing the payload and a e Status Packet Used to acknowledge transactions and to provide a means of error correction As we have already discussed USB is a host centric bus The host initiates all transactions When the host powers up it polls each of the slave devices in turn using the reserved address 0 it assigns each one a unique address and finds out from each device what its speed is and the and type of data transfer it wishes to perform This process is called enumeration and it also takes place whenever a device is plugged into an active network A typical transaction will consist of a number of packets a token indicating the type of data that the host is sending or requiring the data and in some cases an acknowledgement Each packet is preceded by a sync field and followed by an end of packet marker Common USB Packet Fields Data on the USBus is transmitted LSBit first USB packets consist of the following fields e Sync All packets must start with a sync field
99. emise that it stay compatible wich the existing IEEE 488 1 standard The overriding concept used in the IEEE 488 2 specification for the communication between Controllers and instruments is that of precise talking and forgiving listening In other words IEEE 488 2 exactly defined how both IEEE 488 2 Controllers and IEEE 488 2 instruments talk so that a completely IEEE 488 2 compatible system can be highly reliable and efficient The standard also required that IEEE 488 2 devices be able to work with existing IEEE 488 1 devices by accepting a wide range of commands and data formats as a Listener You obtain the true benefits of IEEE 488 2 when you have a completely IEEE 488 2 compatible system Controllers Although IEEE 488 2 had less impact on Controllers than it did on instruments there are several requirements and optional improvements for Controllers that made an IEEE 488 2 Controller a necessary component of test systems IEEE 488 2 precisely defined the way IEEE 488 2 Controllers send commands and data and added functionality Because of these IEEE 488 2 Controller requirements instrument manufacturers can design more compatible and efficient instruments The benefits of this standardization for the test system developer are reduced development time and cost because it solves the problems caused by instrument incompatibilities varying command structures and data formats Requirements of IEEE 488 2 Controllers
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101. endent on the speed of the processor and the particular V XI instruments Local Performance The MXIbus does not degrade the performance of the devices connected to it Each MXI device can operate internally at full speed in parallel with other MXI devices Because MXIbus is a true system bus with multimaster arbitration the only time MXI devices must synchronize their operation is when they perform transactions that map across the MXIbus When one MXI device performs a read or write that maps to a remote MXI device the MXI hardware on both devices interlocks the bus cycle across the MXIbus to accomplish the transfer MXI An Open Standard The MXIbus specification was developed by National Instruments and announced in April 1989 as an open industry standard A VXIplug amp play core technology MXIbus has been endorsed by the entire VXI plug play Systems Alliance including Tektronix Hewlett Packard Racal Instruments and GenRad Because MXI is an open standard documented with a comprehensive specification anyone can develop products that will be integrated into a MXI controlled system 3402438 04 April 1995 14 3 HA What is PXI PXI tutorial Fr n National Instruments Introduction PXI PCI extensions for Instrumentation is a rugged PC based platform for measurement and automation systems PXI combines PCI electrical bus features with the rugged modular Eurocard packaging of CompactPCI and then adds specialized synchr
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103. equirements of the bus it is wise to specify a conservative payload size If you are using a large payload it may also be to your advantage to specify a series of alternative interfaces with varying isochronous payload sizes If during enumeration the host cannot enable your preferred isochronous endpoint due to bandwidth restrictions it has something to fall back on rather than just failing completely Data being sent on an isochronous endpoint can be less than the prenegotiated size and may vary in length from transaction to transaction Isochronous transactions do not have a handshaking stage and cannot report errors or STALL HALT conditions e Bulk Transfers Bulk transfers can be used for large bursty data Such examples could include a print job sent to a printer or an image generated from a scanner Bulk transfers provide error correction in the form of a CRC16 field on the data payload and error detection re transmission mechanisms ensuring data is transmitted and received without error Bulk transfers will use spare un allocated bandwidth on the bus after all other transactions have been allocated If the bus is busy with isochronous and or interrupt then bulk data may slowly trickle over the bus As a result Bulk transfers should only be used for time insensitive communication as there is no guarantee of latency Bulk Transfers are used to transfer large bursty data e have error detection via CRC with guarantee of delivery e No guar
104. est of time Before VISA there were many different commercial implementations of I O software for VXI GPIB and serial interfaces however none of these I O software products were standardized or interoperable lbs Compa ux bu Behpkre Figure 4 VXIbus System Software Components The VISA standard lays the foundation and provides a unified migration path for Industry wide software compatibility One of the most notable benefits of VISA is its ability to significantly reduce the time and effort involved in programming different I O interfaces Instead of using a different Application Programmers Interface API devoted to each interface bus you can use the VISA API regardless of whether your system is controlled by GPIB VXI or a GPIB VXI With the vast number of choices in instrumentation and software now available most users do not want to be locked into a specific vendor for their systems Instead they would prefer the freedom to select the best instruments and software available from multiple vendors and have it all work together with minimal effort The IEEE 488 1 and IEEE 488 2 standards for GPIB and the IEEE 1155 standard for VXT ensured that the hardware would be interoperable but this approach was not taken for the software Therefore the ideal new driver architecture should be a standard adopted by as many of the major vendors as possible Then you could be assured that any code written for your instrument is portable across c
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106. figuration and to provide a valid list of GPIB devices that can be used as the input parameter to all other TEEE 488 2 protocols The bus line monitoring capability of an IEEE 488 2 Controller is also useful to detect and diagnose problems within a test system The FINDRQS protocol is an efficient mechanism for locating and polling devices chat are requesting service It uses the IEEE 488 2 Controller capability of sensing the FALSE to TRUE transition of the SRQ line You prioritize the input list of devices so that the more critical devices receive service first If the application program can jump to this protocol immediately upon the assertion of the SRQ line you increase program efficiency and throughput IEEE 488 2 Instruments The IEEE 488 2 specifications for instruments can require major changes in the firmware and possibly the hardware However IEEE 488 2 instruments are easier to program because they respond to common commands and queries in a well defined manner using standard message exchange protocols and data formats The IEEE 488 2 message exchange protocol is the foundation for the SCPI standard that makes test system programming even easier IEEE 488 2 defines a minimum set of IEEE 488 1 interface capabilities that an instrument must have All devices must be able to send and receive data request service and respond to a device clear message d GPIB Tutorial IEEE 488 2 defines precisely the form
107. he CALCulate block converts application data to account for signal generation anomalies such as correcting for external effects converting units and changing domains Example SCPI Command The following command programs a digital multimeter DMM to configure itself to make an AC voltage measurement on a signal of 20 V with a 0 001 V resolution MEASure VOLTage AC 20 0 001 e The leading colon indicates a new command is coming The keywords MEASure VOLTage AC instruct the DMM to take an AC voltage measurement e The instructs the DMM to return its measurement to the computer controller e The 20 0 001 specifies the range 20 V and resolution 001 V of the measurement Reference Documents For more information on the GPIB standards refer to the following documents ANSI IEEE 488 1 1987 IEEE Standard Digital Interface for Programmable Instrumentation ANSI IEEE 488 2 1992 IEEE Codes Formats Protocols and Common Commands and Standard Commands for Programmable Instruments You can obtain the IEEE 488 specifications by writing to The Institute of Electrical and Electronic Engineers IEEE 345 East 47th St New York NY 10017 USA The latest SCPI Standards are published by the SCPI Consortium Kw Tutorial GPIB Tutorial HSASS The Hi peed GPIB Handshake Protocol National Instruments has developed the patented high speed GPIB handshake protocol called HS488 to increase the data tran
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109. ices not only will the engineer be able to access the field devices but they are also able to communicate with other field devices In essence fieldbus will replace centralised control networks with distributed control networks Therefore fieldbus is much more than a replacement for the 4 20mA analogue standard The fieldbus technology promises to improve quality reduce costs and boost efficiency These promises made by the fieldbus technology are derived partly from the fact that information which a field device is required to transmit or receive can be transmitted digitally This is a great deal more accurate than transmitting using analogue methods which were used previously Each field device is also a smart device and can carry out it s own control maintenance and diagnostic functions As a result it can report if there is a failure of the device or manual calibration is required this increases the efficiency of the system and reduces the amount of maintenance required Each field device will be more flexible as they will have computing power One fieldbus device could be used to replace a number of devices using the 4 20mA analogue standard Other major cost savings from using fieldbus are due to wiring and installation the existing 4 20mA analogue signal standard requires each device to have is own set of wires and its own connection point Fieldbus eliminates this need so only a single twisted pair wiring scheme 1s required
110. ief cannot tap into the network vulnerable points such as the door mirrors to deactivate a car alarm system Audi BMW DaimlerChrysler Motorola Volcano Volvo and Volkswagen cre ated this inexpensive open standard Byteflight A flexible time division multiple access TDMA protocol for safety related applications Byteflight can be used with devices such as air bags and seat belt tensioners Because of its flexi bility Byteflight can also be used for body and con venience functions such as central locking seat motion control and power windows BMW ELMOS Infineon Motorola and Tyco EC collab orated in its development Although not specifically designed for X by wire applications Byteflight is a very high performance network with many of the features necessary for X by wire FlexRay FlexRay is a fault tolerant protocol designed for high data rate advanced control applications such as X by wire systems The pro tocol specification now nearing completion promises time triggered communications a syn chronized global time base and real time data transmission with bounded message latency Proposed applications include chassis control X by wire implementations and body and power train systems BMW DaimlerChrysler Philips and Computer Motorola are collaborating on FlexRay and its sup porting infrastructure FlexRay will be compatible with Byteflight Time triggered CAN As an extension of the CAN protocol tim
111. irements electromagnetic compatibility power distribution cooling and air flow for VXIbus mainframes and plug in modules The modules are installed in the mainframe slots LEDs switches test points and I O connections are accessible from the module front panel Pa ute E Com puter Eus 16 bit date trareter 16 Megeab re stressar y Mu m arer Drbretop Priority rrupt Lies Bus Fe Center Row Adds WHE S2 btdets and Fi gqesbye achte sang P2 Chater Roas X 6 dz 10 MHz lock TIL 4 EL Trigger bus 12 pin Looal bus Arakg Sum bus Module iden ticeton LS Power Distrikter bp ma Pa walad High Per iorrn ere 1h ed o 100 MH cock BCL Star mass bus BOL Trigger bus e pin Gel bus Power Disinburion bus Figure 2 VXI Module Sizes Module and Mainframe Cooling Airflow direction is from bottom P3 to top P1 Cooling requirements must be established for all modules and included in product specifications These requirements must include an operating point of minimum airflow requirement Mainframe suppliers must also provide similar information for their mainframes EMC and Noise The addition of a new module to a VXIbus system must not degrade the performance of any other module The V XIbus specification includes near field radiation and susceptibility requirements which prevent one module from interfering with the operation of other modules To help meet these requirements the VXIbus module width was increased from the 0 8 in VME
112. l hosts have a downstream connection to the device Upstream and downstream connectors are not mechanically interchangeable thus eliminating illegal loopback connections at hubs such as a downstream port connected to a downstream port There are commonly two types of connectors called type A and type B which are shown below Receptical Type B Receptacle Type A ATT Figure 1 USB connectors Type A plugs always face upstream Type A sockets will typically find themselves on hosts and hubs For example type A sockets are common on computer main boards and hubs Type B plugs are always connected downstream and consequently type B sockets are found on devices It is interesting to find type A to type A cables wired straight through and an array of USB gender changers in some computer stores This is in contradiction of the USB specification The only type A plug to type A plug devices are bridges which are used to connect two computers together Other prohibited cables are USB extensions which has a plug on one end either type A or type B and a socket on the other These cables violate the cable length requirements of USB USB 2 0 included errata which introduces mini USB B connectors The details on these connectors can be found in Mini B Connector Engineering Change Notice The reasoning behind the mini connectors came from the range of miniature electronic devices such as mobile phones and organisers The current type B connector is too large to
113. last MXI devices to minimize reflections at the ends of cables MXI uses state of the art single ended trapezoidal bus transceivers to reduce noise crosstalk in the transmission system Designed specifically for driving backplane bus signals these transceivers have open collector drivers that generate precise trapezoidal waveforms with typical rise and fall times of 9 ns The trapezoidal shape due to the constant rise and fall times reduces noise coupling crosstalk on adjacent lines The receiver uses a lowpass filter to remove noise and a high speed comparator that recognizes the trapezoidal shaped signal from the noise Performance Isssues MXIbus Performance It 1s often difficult to understand how a performance specification for a single component relates to the overall performance of your system In the case of MXI it is important to understand not only the performance issues associated with the MXI link but also the devices that communicate across the link MXI works like an embedded computer using a direct hardware memory map to eliminate software overhead between your computer and the VXIbus or VMEbus Both MXI and embedded VXI computers can use shared memory communication protocols and direct register accesses for potentially dramatic performance improvements over GPIB If your VXI instruments themselves do not use these capabilities however your system performance using MXI or an embedded computer may be no higher than a GPIB control
114. led V XI system There are several factors to consider when comparing a MXI equipped computer to an embedded computer A MXT equipped computer is functionally equivalent to an embedded computer In fact application software developed on a MXI computer using NI VXI VISA bus interface software can easily run on an embedded computer and vice versa There are subtle hardware timing differences but there is no dramatic performance difference due to architecture MXI for example can take roughly 100 ns more to perform a single VXI read or write than an embedded computer because the MXI signals must propagate down the MXI cable at 10 ns m This subtle detail is 13 measured in ns and is negligible compared to the other factors that affect your system performance such as the execution speed of your application software or your instruments Often the most important performance issue to consider when evaluating a computer for your system is the performance of the processor itself Most applications spend much more time computing displaying or performing disk I O than actually performing I O across the VXIbus or VMEbus Current external MXI computers are over four times as fast as the fastest embedded VXI computer In addition because of the physical space constraints of embedded computers external computers often have much more sophisticated architectures with faster processors cache RAM faster disk drives and other benefits Raw computing power can
115. ll supply the control link to the wheel mounted steering actuator motors Removal of the steering column will improve driver safety in collisions and allow new styling freedom It will also simplify production of left and right hand models It is natural to add advanced functions to such electronic systems For example consider systems that reduce steering wheel feedback to the driver In mechanical steering systems the driver actually feels the vehicle losing control in unstable conditions and can react appropriately Today such electronic fea tures as antilock braking may let the vehicle approach or surpass this control loss edge without providing warning To accommodate this X by wire systems can include motors on the steering wheel that provide artificial feedback to the driver All major automakers are developing prototype or production X by wire systems TRW s electronic power assisted steering system improves fuel econ omy by up to 5 percent Delphi Automotive Systems claims similar improvements from its E Steer sys Antilock brake system Adaptive cruise control Electronic brakeforce distribution Electronic control unit Electrohydraulic brakes Electromechanical brakes Electronic stability program Hydraulic control unit Traction control system Research potential tem Companies such as Bosch Continental AG Visteon Valeo and most other original equipment manufacturers have either developed or plan to develop X by wir
116. mental Challenges Consumer Opportunities Auto com http www auto com travcity99 wpowers_aug5 htm current Dec 2001 3 G Leen D Heffernan and A Dunne Digital Net works in the Automotive Vehicle IEE Computer and Control Eng J Dec 1999 pp 257 266 System Peak load Electromechanical valves 2 400 Water pump 300 Engine cooling fan 800 Power steering all electric 1 000 Heated windshield 2 000 Preheated catalytic converter 3 000 Active suspension 12 000 Onboard computing navigation Total average 4 Electronic Brake Management ALex Current Fact book BMW Research and Development http www bmwgroup com e index2 shtml s50820_0_www_bm weroup_com 4_news 4_4_aktuelles_lexikon 4_4_akt uelles_lexikon shtml current Dec 2001 5 A van Zanten et al ESP Electronic Stability Pro gram Robert Bosch GmbH Stuttgart Germany 1999 6 T Thurner et al X By Wire Safety Related Fault Tolerant Systems in Vehicles Document No XBy Wire DB 6 6 25 X by Wire Consortium Stuttgart Germany 1998 7 J M Miller Multiple Voltage Electrical Power Dis tribution Systems for Automotive Applications Proc 31st Intersociety Energy Conversion Conf IEEE Press Piscataway N J 1996 pp 1930 1937 8 J G Kassakian Automotive Electrical Systems The Power Electronics Market of the Future Proc Applied Power Electronics Conf and Exposition APEC 2000 IEEE Press Piscataway N J 2000 pp 3
117. more associated lower level devices or Servants A Servant is any device in the subtree of a Commander A device can be both a Commander and a Servant in a multiple level hierarchy A Commander has exclusive control of the communication and configuration registers of its immediate Servants one or more Any VXI module has one and only one Commander Commanders communicate with Servants through the communication registers of the Servants using the Word Serial Protocol if the Servant is a Message Based device or by device specific register manipulation if the Servant is a Register Based device Servants communicate with their Commander by responding to the Word Serial commands and queries from their Commander through the Word Serial protocol if they are Message Based or by device specific register status if they are Register Based Interrupts and Asynchronous Events Servants can communicate asynchronous status and events to their Commander through hardware interrupts or by writing specific messages signals directly to their Commander s hardware Signal Register Nonbusmaster devices always transmit such information via interrupts whereas devices that have busmaster capability can either use interrupts or send signals Some Commanders can receive signals only whereas others might be only interrupt handlers The VXIbus specification contains defined Word Serial commands so that a Commander can understand the capabilities of its Message Based Servan
118. munications channel at the USB function At the software layer your device driver may send a packet to your devices EP1 for example As the data is flowing out from the host it will end up in the EP1 OUT buffer Your firmware will then at its leisure read this data If it wants to return data the function cannot simply write to the bus as the bus is controlled by the host Therefore it writes data to EP1 IN which sits in the buffer until such time when the host sends a IN packet to that endpoint requesting the data Endpoints can also be seen as the interface between the hardware of the function device and the firmware running on the function device All devices must support endpoint zero This is the endpoint which receives all of the devices control and status requests during enumeration and throughout the duration while the device is operational on the bus Pipes While the device sends and receives data on a series of endpoints the client software transfers data through pipes A pipe is a logical connection between the host and endpoint s Pipes will also have a set of parameters associated with them such as how much bandwidth is allocated to it what transfer type Control Bulk Iso or Interrupt it uses a direction of data flow and maximum packet buffer sizes For example the default pipe is a bi directional pipe made up of endpoint zero in and endpoint zero out with a control transfer type USB defines two types of pipes e Stream Pipes have
119. nd triggering buses Figure 2 Using these timing and triggering buses users can develop systems for applications requiring precise synchronization Star Trigger Bus THU UU Fromm ULL r lt E G Local Bus lt 132 Mbytes s 33 MHz 32 bit PCI Bus gt lt PXI Trigger Bus gt Figure 2 PXI Timing and Triggering Buses PXI combines industry standard PC components such as the PCI bus with advanced triggering and synchronization extensions on the backplane zu as gt wo c Star Trigger Controller PXI Controllers As defined by the PXI Hardware Specification all PXI chassis contain a system controller slot located in the leftmost slot of the chassis slot 1 Controller options include remote controllers from a desktop workstation server or a laptop computer and high performance embedded controllers with either a Microsoft OS Windows 2000 XP or a real time OS LabVIEW Real Time PXI Remote Controllers There are two types of PXI remote controllers Laptop control of PXI PC control of PXI Laptop Control of PXI With ExpressCard MXI Measurement eXtensions for Instrumentation and PCMCIA CardBus interface kits users can control PXI systems directly from laptop computers During boot up the laptop computer will recognize all peripheral modules in the PXI system as PCI devices Figure 3 Laptop Control of PXI PCMCIA CardBus interface kit top and Exp
120. ndicate the type of transaction to follow data packets contain the payload handshake packets are used for acknowledging data or reporting errors and start of frame packets indicate the start of a new frame e Token Packets There are three types of token packets In Informs the USB device that the host wishes to read information Out Informs the USB device that the host wishes to send information Setup Used to begin control transfers Token Packets must conform to the following format Sync PID ADDR oer crcs EOP e Data Packets There are two types of data packets each capable of transmitting 0 to 1023 bytes of data called Data0 and Datal Data packets have the following format Sync pio Ge cRct6 er e Handshake Packets There are three type of handshake packets which consist simply of the PID ACK Acknowledgment that the packet has been successfully received NAK Reports that the device cannot send nor received data temporary Also used during interrupt transaction to inform the host there is no data to send STALL The device finds its in a state that it requires intervention from the host Handshake Packets have the following format Sync PID er e Start of Frame Packets The SOF packet consisting of an 11 bit frame number is sent by the host every 1mS 500nS sme PID Frame Number crcs er _ USB Functions When we think of a USB device we think of a USB peripheral b
121. nels such as shared memory channels can be established to take advantage of the VXIbus bandwidth capabilities Word Serial Protocol The VXIbus Word Serial Protocol is functionally very similar to the IEEE 488 protocol which transfers data messages to and from devices one byte or word at a time Thus VXI Message Based devices communicate in a fashion very similar to IEEE 488 instruments In general Message Based devices typically contain some level of local intelligence that uses or requires a high level of communication All VXI Message Based devices are required to use the Word Serial Protocol to communicate in a standard way The protocol is called word serial because if you want to communicate with a Message Based device you do so by writing and reading 16 bit words one at a time to and from the Data In write Data Low and Data Out read Data Low hardware registers located on the device itself Word Serial communication is paced by the bits in the response register of the device indicating whether the Data In register is empty and whether the Data Out register is full This operation is very similar to Universal Asynchronous Receiver Transmitter UART on a serial port Commander Servant Hierarchies The VXIbus defines a Commander Servant communication protocol so you can construct hierarchical systems using conceptual layers of VXI devices This structure is like an inverted tree A Commander is any device in the hierarchy with one or
122. ng Error Frames The Overload Frame The Overload Frame is mentioned here just for completeness It is very similar to the Error Frame and is transmitted by a node that becomes too busy The Overload Frame is not used very often as today s CAN controllers are clever enough not to use it CAN Physical Layer s A physical layer defines the electrical levels and signaling scheme on the bus the cable impedance and similar things There are a few different physical layers e ISO 11898 defines a two wire balanced signaling scheme e Little used ISO 11519 for lower speed applications defines another two wire balanced signaling scheme for lower bus speeds e Several proprietary physical layers do exist e A modified type of RS485 has been used Most CAN transceiver chips are manufactured by Philips alternative vendors include Siliconix and Unitrode A very common type is the 82C250 transceiver which implements the physical layer defined by ISO 11898 The ISO 11898 prescribes that the cable impedance be nominally 120 Ohms an impedance in the interval of 108 132 Ohms is permitted There are not many cables in the market today that fulfils this requirement There is a good chance that the allowed impedance interval will be broadened in the future see CANHUG s proposal The maximum speed of a CAN bus according to the standard is I Mbit second At this speed a maximum cable length of about 40 metres 130 ft can be used Thi
123. ng a benefit of roughly 0 2 km liter or 0 4 mpg Its lite hybrid alterna tor starter will operate the vehicle in start and stop mode in which the engine can be restarted in 200 ms for even more fuel savings In addition removal of the front end accessory drive running the alternator and power steering pump will mean enhanced car styling The new 42 V systems are expected in new autos by 2003 Within the electrical system boosting the volt age proportionally reduces the required current for a given delivered power Smaller currents will use smaller and lighter gauge cables allowing an expected 20 percent reduction in cable bundle size Further the carrying capacity of semiconductor switches for electrical currents relates directly to silicon area size while operational voltage levels are a function of device thickness and doping pro file With less silicon area required these systems will achieve a significant cost reduction in solid state load switching devices The 42 V systems will require a 36 V battery and produce a maximum operating level of 50 V with a maximum dynamic overvoltage of 58 V Engineers regard a 60 V limit as the safe maximum for cars greater voltages can generate shocks Despite the obvious advantages of 42 V systems challenges loom Transition costs reengineering of products and production processes will be extremely high due to the legacy of a half century of 12 V systems The upgrading
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125. nown as High Speed mode and was a tack on to compete with the Firewire Serial Bus In conclusion there are three data transfer speeds defined within the USB standard High Speed 480Mbits s e Full Speed 12Mbits s e Low Speed 1 5Mbits s The Universal Serial Bus is host controlled and there can only be one host per bus The specification in itself does not support any form of multi master arrangement However the On The Go specification which is a tack on standard to USB 2 0 has introduced a Host Negotiation Protocol which allows two devices negotiate for the role of host This is aimed at and limited to single point to point connections such as a mobile phone and personal organiser and not multiple hub multiple device desktop configurations The USB host is responsible for undertaking all transactions and scheduling bandwidth Data can be sent by various transaction methods using a token based protocol USB uses a tiered star topology similar to that of 10BaseT Ethernet This imposes the use of a hub somewhere which adds to greater expense more boxes on your desktop and more cables However it is not as bad as it may seem as many devices have USB hubs integrated into them For example your keyboard may contain a hub which is connected to your computer Your mouse and other devices such as your digital camera can be plugged easily into the back of your keyboard Monitors are just another peripheral on a long list which commonly have
126. ntegration e Modular rugged design improves reliability increases mean time between failure MTBF and decreases mean time to repair MTTR Members of the VXIbus Consortium and the VXIplug amp play Systems Alliance have combined their expertise to develop technically sound standards for both hardware and software bringing the entire industry into a new generation of easy to use instrumentation The Value of Open Industry Standards The baseline VXI hardware specifications are a mandate for interoperatibility between hardware products from different vendors These specifications cover mechanical and environmental requirements such as module sizes mainframe and module cooling and EMC compatibility between modules as well as automated system initialization and backplane communication protocols The VXIplug amp play Systems Alliance builds on these baseline specifications to address the system as a whole with the goal of having the end user up and running in Five minutes or less Building a system based on open industry standards means that you choose components for your system based on your requirements regardless of vendor Open standards also ensure that once your system is built your investment will continue to pay dividends well into the future Both the VXI Consortium and the V XIplug amp play Systems Alliance remain strong active organizations committed to maintaining VXI as an open multivendor technology and increasing its ease of
127. ntroller monitors the communications network GPIB When 5 Interface the center Controller notices that a party Management Lines device wants to make a call send a data message it connects the caller Talker to the receiver Listener Grounds The Controller usually addresses or enables a Talker and a Listener before the Talker can send its message to the Listener After the message is transmitted the Controller may Figure 2 GPIB Signals and Lines address other Talkers and Listeners SS PHONE 512 794 0100 e FAX 512 794 8411 e info natinst com e www natinst com NATIONAL INSTRUMENTS 4 11 Tut GPIB Tutorial 18 GND Twisted Pair with DAV 6 NRFD 7 T 19 1 GND Twisted Pair with NRFD a T 20 GND Twisted Pair with NDAC s T 21_ GND Twisted Pair with IFC sRo 10 T 22 GND Twisted Pair with SRQ ATN 111 23 GND Twisted Pair with ATN SHIELD TZT 22 SIGNAL GROUND Figure 3 GPIB Connector and Signal Assignment Some GPIB configurations do not require a Controller For example a device that is always a Talker called a talk only device is connected to one or more listen only devices A Controller is necessary when the active or addressed Talker or Listener must be changed The Controller function is usually handled by a computer A computer equipped with National Instruments GPIB hardware and software can perform the roles of Talker Listener and Controller The Cont
128. ode doesn t participate in the bus traffic at all Using the error counters a CAN node can not only detect faults but also perform error confinement The CAN controller s habit of automatically retransmitting messages when errors have occurred can be annoying at times There is at least one controller on the market the SJA 1000 from Philips that allows for full manual control of the error handling The Layout of a Bit From a programmer s point of view each bit on the CAN bus is divided into at least 4 quanta The quanta are logically divided into four groups or segments e the Start Segment e the Propagation Segment e the Phase Segment 1 e the Phase Segment 2 The bus levels are sampled at the border between Phase Segment 1 and Phase Segment 2 Most CAN controllers also provide an option to sample three times during a bit In order to adjust the on chip bus clock the CAN controller may shorten or prolong the length of a bit by an integral number of quanta The maximum value of these bit time adjustments are termed the Synchronization Jump Width SJW IN VEHICLE NETWORKS Gabriel Leen PEI Technologies Donal Heffernan University of Limerick Expanding Automotive Electronic Systems UTCOUN ES A vast increase in automotive electronic systems coupled with related demands on power and design has created an array of new engineering opportunities and challenges he past four decades have witnessed an
129. onization buses and key software features PXI is both a high performance and low cost deployment platform for measurement and automation systems These systems serve applications such as manufacturing test military and aerospace machine monitoring automotive and industrial test Developed in 1997 and launched in 1998 PXI was introduced as an open industry standard to meet the increasing demands of complex instrumentation systems Today PXI is governed by the PXI Systems Alliance PXISA a group of more than 65 companies chartered to promote the PXI standard ensure interoperability and maintain the PXI specification For more information on the PXISA including the PXI specification refer to the PXISA website at www pxisa org Hardware Architecture PXI systems are comprised of three basic components chassis system controller and peripheral modules Chassis VW NI PXI 1042 a D JE FETE Sia m y z engen a y y Tos y y Foz A x Modules Controller 8 T DN Figure 1 A standard 8 Slot PXI chassis contains an embedded system controller and seven peripheral modules PXI Chassis The chassis provides the rugged and modular packaging for the system Chassis generally ranging in size from 4 slots to 18 slots are also available with special features such as DC power supplies and integrated signal conditioning The chassis contains the high performance PXI backplane which includes the PCI bus and timing a
130. onous data transfer method that increases MXIbus throughput for block data transfers From a system standpoint this means that MXI throughput rates can easily keep up with the data rates of high performance computers peripherals and instrumentation From a user standpoint this translates to increased performance and reduced time to test By choosing a PC based MXI approach you are choosing to add value to your VXI instrumentation systems by leveraging technologies that make sense from both a cost and performance perspective 10 MXIbus Applications You can use MXIbus for a variety for a variety of applications You can interface industry standard desktop computers to VXIbus or VMEbus you can create multiple chassis configurations using our VXI MXI or VME MXI extenders and you can integrate VXI and VME chassis into the same test system Figures 5 and 6 show two common configurations with MXIbus Edem al Com puter To Liter ela T arn Figure 5 PC Using MXI to Control a VXIbus System WX errar Embedded i PO Resource hara ger Mix bea Figure 6 MXI Used for Multiple Mainframe VXI System 11 How Does MXIbus Work MXTIbus is a general purpose 32 bit multimaster system bus on a cable MXI interconnects multiple devices using a flexible cabling method similar to GPIB but uses a hardware memory mapped communication scheme that eliminates the software overhead MXI devices can directly access each other s resources by pe
131. ontroller vendors as well as operating systems This is exactly what the VXIplug amp play Systems Alliance has done with VISA MXI Tutorial This section contains an overall introduction to MXI MXIbus Overview The MXI bus is a powerful high speed communication link that interconnects devices using a flexible cabling scheme Derived from the VMEbus MXI provides a high performance way of controlling VXI systems using commercially available desktop computers and workstations National Instruments developed and published the MXI specification and released it as an open industry standard in 1989 In 1995 National Instruments introduced MXI 2 which offers even higher performance A MXIbus system configuration combines the performance benefits of a custom embedded VXI computer with the flexibility and availability of general purpose computers The MXIbus system configuration uses the high speed MXTIbus cable to connect an external computer directly to the VXI backplane With the MXIbus you can locate the computer directly next to the VXI mainframe or up to 20 meters away Using the MXIbus you can easily add other VXI mainframes and use the plug in slots in the external computer for GPIB control plug in DAQ boards or other peripheral adapter cards For instrument control MXI complements high speed platforms such as PCI by harnessing their high throughput potential PCI based desktop PCs compete with the most advanced computer workstations to pr
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133. or an industry standard instrument on a card architecture has been driven by the need for physical size reduction of rack and stack instrumentation systems tighter timing and synchronization between multiple instruments and faster transfer rates than the I Mbytes s rate of the 8 bit GPIB The modular form factor high bandwidth and commercial success of the VMEbus made it particularly attractive as an instrumentation platform The tremendous popularity of GPIB also made it attractive as a model for device communication and instrument control protocols The V XIbus specification adds the standards necessary to combine the VMEbus with GPIB to create a new modular instrumentation platform that can meet the needs of future instrumentation applications Product and company names are trademarks or trade names of their respective companies 340243B 01 Copyright 1996 National Instruments Corporation All rights reserved April 1996 VXI brings the following benefits to instrumentation users e Open multivendor standards maximize flexibility and minimize obsolescence e Increased system throughput reduces test time and or increases capabilities e Smaller size and higher density reduce floor space enhance mobility or portability and give close proximity to devices s being tested or controlled e More precise timing and synchronization improve measurement capability e Standardized VXIplug amp play software eases system configuration programming and i
134. ore than 10 years ago which the Optical Chip Consortium consisting of C amp C Electronics Becker and others has promoted since 1992 D2B was designed for audio video communications computer peripherals and automotive media appli cations The Mercedes Benz S class vehicle uses the D2B optical bus to network the car radio autopi lot and CD systems the Tele Aid connection cel lular phone and Linguatronic voice recognition application Bluetooth Bluetooth is an open specification for an inexpensive short range 10 100 meters low power miniature radio network The protocol pro vides easy and instantaneous connections between Bluetooth enabled devices without the need for cables Potential vehicular uses for Bluetooth include hands free phone sets portable DVD CD and MP3 drives diagnostic equipment and hand held computers Mobile media link Designed to support automotive multimedia applications the mobile media link net work protocol facilitates the exchange of data and control information between audio video equip ment amplifiers and display devices for such things as game consoles and driver navigation maps Delphi Packard Electric Systems developed the MML protocol based on a plastic fiber optic phys ical layer Delphi has installed the system in the Network Vehicle an advanced concept vehicle developed in conjunction with IBM Sun Micro systems and Netscape Figure 1 One sub set of a modern vehicle
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136. ovide a low cost platform that delivers superior performance You can use low cost desktop computers to control sophisticated VXI instrumentation without sacrificing performance or control More importantly as new desktop computers incorporate the latest technology including faster more capable microprocessors and RAM you can easily upgrade your VXI system as these newer and faster computers emerge to immediately reap increased V XI performance gains Thus a PCI based MXI 2 solution such as our VXI PCI8000 gives you excellent performance now with headroom for the future A New Generation of VXI Connectivity Many VXI users migrate from GPIB based systems As a result the National Instruments GPIB V XI is a popular way to control VXI instruments from a GPIB controller An increasingly popular way to control VXI however is to use a custom V XI computer that plugs directly into the VXI mainframe such as the National Instruments VXIpe and VXIcpu Series of embedded VXI computers This embedded approach is technically attractive because the computer communicates directly with the VXIbus and is tightly coupled to the Instruments Although an embedded computer is very powerful custom VXI computers cannot possibly keep pace with the general purpose computer market In the last decade specialized Instrument controllers have rapidly declined General purpose PCs and workstations with their vast array of software and accessories have revolutionized
137. ressCard MXI interface kit bottom The ExpressCard MXI interface kit provides a 110 MB s PCI Express to PCI bridge from the laptop computer to the PXI chassis The PCMCIA CardBus interface kit provides a 50 MB s PCI to PCI bridge from the laptop computer to the PXI chassis Users now have the advantage of mobile portable PXI systems with laptop control of PXI You can purchase any ExpressCard MXI compatible laptop or PCMCIA CardBus compatible laptop to remotely control your PXI system PC Control of PXI With MXI Express and MXI 4 interface kits users can control PXI systems directly from desktop workstation or server computers During boot up the computer will recognize all peripheral modules in the PXI system as PCI devices Figure 4a Remote control with 2 port MXI Express provides simultaneous control of two PXI chassis with combined 160 MB s throughput The MXI Express interface kit provides a 110 MB s PCI Express to PCI bridge from the PC to the PXI chassis With the NI PXI PCle8362 2 port interface kit users will be able to control two PXI systems simultaneously from a single PC Figure 4b Remote control with MXI 4 provides PC control of PXI as well as multichassis PXI systems The MXI 4 interface kit provides a 78 MB s PCI to PCI bridge from PC to the PXI system MXI 4 interface kit comes with low cost copper links or fiber optic links for both extended distances and electrical isolation As shown in Figure 4b yo
138. rforming simple read and writes to appropriate address locations The new MXI 2 standard expands on the MXI 1 standard by exporting all VXI backplane signals such as VXI defined trigger lines interrupt lines and system clocks in addition to the standard MXIbus signals directly to the cabled bus MXI 2 users can accomplish critical timing and synchronization tasks between up to eight daisy chained MXI devices MXI device connectivity is accomplished at the hardware level The MXI cable serves as a transparent link that interconnects multiple MXI devices These devices are interlaced by mapping together portions of their individual address spaces so that a system composed of multiple devices behaves as a single system with a shared address space Figure 7 shows the MXIbus hardware memory mapped communication The immediate benefit of this approach is increased data throughput due to the absence of software overhead Each MXTIbus hardware interface has address window circuitry that detects internal local bus cycles that map out to the MXIbus In addition this circuitry also detects external remote MXIbus cycles of connected devices whose addresses map into the shared memory space of the overall system When a hardware write or read occurs with an address that maps across MXI the MXI hardware interlocks the bus cycle between the devices via the MXIbus This hardware scheme is the same as that used by embedded VXI controllers Plus Uewe Pele bus Cem
139. ric parameters e g M K or u If only specific numeric values are accepted the multimeter will automatically round the input numeric parameters The following command uses a numeric parameter VOLTage DC RANGe lt range gt MINimum MAXimum Discrete Parameters Discrete parameters are used to program settings that have a limited number of values like BUS IMMediate EXTernal They have a short form and a long form just like command keywords You can mix upper and lower case letters Query responses will always return the short form in all upper case letters The following command uses discrete parameters TRIGger SOURce BUS IMMediate EXTernal Chapter 4 Remote Interface Reference Output Data Formats Boolean Parameters Boolean parameters represent a single binary condition that is either true or false For a false condition the multimeter will accept OFF or 0 For a true condition the multimeter will accept ON or 1 When you query a boolean setting the instrument will always return 0 or 1 The following command uses a boolean parameter INPut IMPedance AUTO OFF ON String Parameters String parameters can contain virtually any set of ASCII characters A string must begin and end with matching quotes either with a single quote or with a double quote You can include the quote delimiter as part of the string by typing it twice without any characters in between The following command uses
140. roller in Charge and System Controller Although there can be multiple Controllers on the GPIB at any time only one Controller is the Controller In Charge CIC Active control can be passed from the current CIC to an idle Controller Only the System Controller can make itself the CIC The National Instruments GPIB board is usually the System Controller GPIB Signals and Lines The GPIB interface system consists of 16 signal lines and eight ground return or shield drain lines The 16 signal lines discussed below are grouped into data lines eight handshake lines three and interface management lines five see Figure 2 4 12 NATIONAL INSTRUMENTS Data Lines The eight data lines DIO1 through DIOS carry both data and command messages The state of the Attention ATN line determines whether the information is data or commands All commands and most data use the 7 bit ASCII or ISO code set in which case the eighth bit DIO8 is either unused or used for parity Handshake Lines Three lines asynchronously control the transfer of message bytes between devices The process is called a 3 wire interlocked handshake It guarantees that message bytes on the data lines are sent and received without transmission error e NRFD not ready for data Indicates when a device is ready or not ready to receive a message byte The line is driven by all devices when receiving commands by Listeners when receiving data messages
141. roughput who knows what tomorrow may hold How can you take these benefits both now and in the future We believe that the answer is MXI MXI provides you with a solution that combines the performance benefits of an embedded VXI computer with the flexibility of a general purpose desktop computer Our VXI PCI8000 controller and our next generation MXI 2 provides you with an ultra high performance VXI connectivity solution that can meet your needs both today and well into the future Although traditional connectivity solutions have proved to be very effective they also have proved to be the bottleneck in V XI test systems because the software protocol overhead associated with these methods significantly reduced the achievable throughput on the link Using MXI this bottleneck is eliminated altogether because MXI devices are connected at the hardware level by mapping each physically separate system into a shared memory space Physically separate devices transparently share resources through simple reads and writes to the appropriate address in memory Our next generation MXI 2 products enhance VXI connectivity by defining a single memory mapped backplane on a bus that can transparently extend bus level I O V XI triggering interrupts and systems clocks between systems You can now use a single cable to conveniently share trigger and timing information between mainframes in a multiple mainframe configuration The MXI 2 0 specification also defines a synchr
142. s A command string sent to the multimeter must terminate with a lt new line gt character The IEEE 488 EOI end or identify message is interpreted as a lt new line gt character and can be used to terminate a command string in place of a lt new line gt character A lt carriage return gt followed by a lt new line gt is also accepted Command string termination will always reset the current SCPI command path to the root level 17 _ Chapter 4 Remote Interface Reference An Introduction to the SCPI Language IEEE 488 2 Common Commands The IEEE 488 2 standard defines a set of common commands that perform functions like reset self test and status operations Common commands always begin with an asterisk are four to five characters in length and may include one or more parameters The command keyword is separated from the first parameter by a blank space Use a semicolon to separate multiple commands as shown below ARST CLS ESE 323 OPC SCPI Parameter Types The SCPI language defines several different data formats to be used in program messages and response messages Numeric Parameters Commands that require numeric parameters will accept all commonly used decimal representations of numbers including optional signs decimal points and scientific notation Special values for numeric parameters like MINimum MAXimum and DEFault are also accepted You can also send engineering unit suffixes with nume
143. s you can exchange an instrument that makes a particular measurement with another instrument capable of making the same measurement without changing the SCPI command The MEASurement component is subdivided into three distinct parts INPut SENSe and CALCulate The INPut NATIONAL INSTRUMENTS 4 17 oj p S GPIB Tutorial AA 7 C0e zz component conditions the incoming signal before it is converted into data by the SENSe block INPut functions include filtering biasing and attenuation The SENSe component converts signals into internal data that you can manipulate SENSe functions control such parameters as range resolution gate time and normal mode rejection The CALCulate component converts the acquired data into a more useful format for a particular application CALCulation functions include converting units rise time fall time and frequency parameters The signal generation component converts data into output as physical signals SCPI subdivides the signal generation block into three function blocks OUTPut SOURce and CALCulate The OUTPut block conditions the outgoing signal after it is generated OUTPut block functions include filtering biasing and attenuation The SOURce block generates a signal based on specified characteristics and internal data SOURce block functions specify such signal parameters as amplitude modulation power current voltage and frequency T
144. s in the messages instead the messages can be said to be contents addressed that is their contents implicitly determines their address Message Types There are four different message types or frames on a CAN bus e the Data Frame e the Remote Frame e the Error Frame and e the Overload Frame The Data Frame The Data Frame is the most common message type It comprises the following important parts a few details are omitted for the sake of brevity e the Arbitration Field which determines the priority of the message when two or more nodes are contending for the bus The contents of the Arbitration field which is 11 or 29 bits long is usually called the Identifier however there is no obligation that the Arbitration field really contains any kind of identifier e the Data Field which contains zero to eight bytes of data e the CRC Field which contains a 16 bit checksum calculated on most parts of the message This checksum is used for error detection e an Acknowledgement Slot any CAN controller that has been able to correctly receive the message sends an Acknowledgement bit at the end of each message The transmitter checks for the presence of the Acknowledge bit and retransmits the message if no acknowledge was detected It is worth noting that the presence of an Acknowledgement Bit on the bus does not mean that any of the intended addressees has received the message just that one node on the bus has received i
145. s is because the arbitration scheme requires that the wave front can propagate to the most remote node and back again before the bit is sampled In other words the cable length is restricted by the speed of light A proposal to increase the speed of light has been considered but was turned down because of its inter galactic consequences Other maximum cable lengths are these values are approximate e 100 metres 330 ft at 500 kbp s e 200 metres 650 ft at 250 kpb s e 500 metres 1600 ft at 125 kbp s e 6 kilometres 20000 ft at 10 kbit s Some CAN controllers will handle higher speeds than 1 Mbit s and may be considered for special applications CAN connectors There is no standard at all Usually each Higher Layer Protocol defines one or a few preferred connector types Common types include e 9 pole DSUB proposed by CiA e 5 pole Mini C and or Micro C used by DeviceNet and SDS e 6 pole Deutch connector proposed by CANHUG for mobile hydraulics Standard vs Extended CAN Originally the CAN standard defined the length of the Arbitration Field to eleven 11 bits Customer demand forced an extension of the standard The new format is often called Extended CAN and allows no less than twenty nine 29 bits in the Arbitration Field The standards are formally called e 2 0A with 11 bit Arbitration Field only e 2 0B extended version with the full 29 bit or the old 11 bit you can mix them Arbitration Field A 2 0B
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148. section 9 1 2 of the USB specification However when writing USB firmware for the first time it is handy to know exactly how the host responds during enumeration rather than the general enumeration process detailed in the specification A common Windows enumeration involves the following steps 1 The host or hub detects the connection of a new device via the device s pull up resistors on the data pair The host waits for at least 100ms allowing for the plug to be inserted fully and for power to stabilise on the device 2 Host issues a reset placing the device is the default state The device may now respond to the default address zero 3 The MS Windows host asks for the first 64 bytes of the Device Descriptor 4 After receiving the first 8 bytes of the Device Descriptor it immediately issues another bus reset 5 The host now issues a Set Address command placing the device in the addressed state 6 The host asks for the entire 18 bytes of the Device Descriptor 7 It then asks for 9 bytes of the Configuration Descriptor to determine the overall size 8 The host asks for 255 bytes of the Configuration Descriptor 9 Host asks for any String Descriptors if they were specified At the end of Step 9 Windows will ask for a driver for your device It is then common to see it request all the descriptors again before it issues a Set Configuration request The above enumeration process is common to Windows 2000 Windows XP and Windows 98
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150. sfer rate of a GPIB system All devices involved in a data transfer must be HS488 compliant to use the HS488 protocol but when non HS488 devices are involved the HS488 devices automatically use the standard IEEE 488 1 handshake to ensure compatibility HS488 is a superset of the IEEE 488 standards HS488 has been proposed as an addition to the IEEE 488 1 standard and is currently being considered by the Working Group for Higher Performance IEEE 488 1 IEEE 488 Handshake The standard IEEE 488 1 3 wire handshake shown in Figure 7 requires the Listener to unassert Not Ready for Data NRED the Talker to assert the Data Valid DAV signal to indicate to the Listener that a data byte is available and for the Listener to unassert the Not Data Accepted NDAC signal when it has accepted that byte A byte cannot transfer in less than the time it takes for the following events to occur NRED to propagate to the Talker DAV signal to propagate to all Listeners the Listeners to accept the byte and assert NDAC the NDAC signal to propagate back to the Talker and the Talker to allow a settling time T1 before asserting DAV again HS488 Handshake HS488 increases system throughput by removing propagation delays associated with the 3 wire handshake To enable the HS488 handshake the Talker pulses the NRED signal line after the Controller addresses all Listeners If the Listener is HS488 capable then the transfer occurs using th
151. such as the amount of power this particular configuration uses if the device is self or bus powered and the number of interfaces it has When a device is enumerated the host reads the device descriptors and can make a decision of which configuration to enable It can only enable one configuration at a time For example it is possible to have a high power bus powered configuration and a self powered configuration If the device is plugged into a host with a mains power supply the device driver may choose to enable the high power bus powered configuration enabling the device to be powered without a connection to the mains yet if it is connected to a laptop or personal organiser it could enable the second configuration self powered requiring the user to plug your device into the power point The configuration settings are not limited to power differences Each configuration could be powered in the same way and draw the same current yet have different interface or endpoint combinations However it should be noted that changing the configuration requires all activity on each endpoint to stop While USB offers this flexibility very few devices have more than one configuration DeviceDescnptor Configuration Configuration Descriptor Descriptor bNuminteraces bMuminterfaces Interface Interface Descriptor Interface Descriptor Interface Descriptor Descriptor bNumEndpoints bNumEndpoints bNumEndpoints bNumEndpoints
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153. t correctly The Remote Frame The Remote Frame is just like the Data Frame with two important differences e itis explicitly marked as a Remote Frame a certain control bit is used for this purpose and e there is no Data Field The intended purpose of the Remote Frame is to solicit the transmission of the corresponding Data Frame If say node A transmits a Remote Frame with the Arbitration Field set to 234 then node B if properly initialized might respond with a Data Frame with the Arbitration Field also set to 234 This can be used to implement a type of request response type of bus traffic management In practice however the Remote Frame is little used It is also worth noting that the CAN standard does not prescribe the behaviour outlined here Most CAN controllers can be programmed either to automatically respond to a Remote Frame or to notify the local CPU instead Sometimes it is claimed that the node responding to the Remote Frame is starting its transmission as soon as the identifier is recognized thereby filling up the empty Remote Frame This is not the case The Error Frame Simply put the Error Frame is a special message that violates the rules of CAN It is transmitted when a node detects a fault and will cause all other nodes to detect a fault The transmitter can then retransmit the message There is an elaborate scheme of error counters that ensures that a node can t destroy the bus traffic by repeatedly transmitti
154. terchange instruments SCPI is a complete yet extendable standard that unifies the software programming commands for instruments The first version of the standard was released in mid 1990 Today the SCPI Consortium continues to add commands and functionality to the SCPI standard SCPI has its own set of required common commands in addition to the mandatory IEEE 488 2 common commands and queries Although Signal Routing Measurement Function Signal fra INPut ee ENSe RG CALCulate _ FORMat Routing ee Der ya i data bus TRIGger MEMory DISPlay SOURce Signal Generation CALCulate FORMat I data bus Figure 10 The SCPI Instrument Model IEEE 488 2 is used as its basis SCPI defines programming commands that you can use with any type of hardware or communication link SCPI specifies standard rules for abbre viating command keywords and uses the IEEE 488 2 message exchange protocol rules to format commands and parameters You may use command keywords in their long form MEASure or their short form shown in capital letters MEAS SCPI offers numerous advantages to the test engineer One of these is that SCPI provides a comprehensive set of programming functions covering all the major functions of an instrument This standard command set ensures a higher degree of instrument interchangeability and minimizes the effort involved in designing new test systems The SCPI command set is hierarchical so a
155. tes and headless operation no keyboard mouse or monitor System Configuration The fastest and easiest way to specify and configure your new PXI system is by using the online PXI Advisor or PXI SCXI Advisor The advisors lead you through a series of questions to help you build your new PXI system with a system controller software modules accessories and PXI or PXI SCXI combination chassis You build your system by answering simple questions and selecting the products best suited to your needs and you can print or export the image of your PXI system for use in proposals or design reviews Additionally the advisors will make recommendations on technical matters such as specific slot placement of modules cables and terminal accessories and integrated software packages The advisors also use behind the scenes logic to prevent incompatible configurations For example if you select a LabVIEW Real Time PXI controller the advisors will automatically restrict PXI measurement module selection to only those compaatible with LabVIEW Real Time When you are satisfied with your configuration you can pass that configuration to a National Instruments representative for order or you can automatically order through the online store With NI Factory Installation Services as part of your order you will receive your PXI system just as you configured it NI installs your selected PXI modules in your chassis and installs any memory upgrades National Ins
156. that combine a number of control sequences to perform common test system operations IEEE 488 2 defines two required protocols and six optional protocols as shown in Table 2 These protocols reduce development time because they combine several commands to execute the most common operations required by any test system The RESET protocol ensures that the GPIB has been initialized and all devices have been cleared and set to a known state The ALLSPOLL protocol serial polls each device and returns the status byte of each device The PASSCTL and REQUESTCTL protocols pass control of the bus between a number of different devices The TESTSYS protocol instructs each device to run its own self tests and report back to the Controller whether it has a problem or is ready for operation NATIONAL INSTRUMENTS 4 15 enoni Tutorial Wawas GPIB Tutorial N lt gt System Data Identification query Internal Operations Reset Internal Operations Self test query Synchronization Operation complete Synchronization Operation complete query Synchronization Wait to complete Status and Event Status and Event Status and Event Status and Event Status and Event Status and Event Status and Event Clear status Event status enable Event status enable query Event status register query Service request enable Service request enable query Read status byte quer Table 3 IEEE 488
157. the host polls it before it can report that it needs urgent attention Interrupt Transfers are unidirectional and use a stream pipe This type of transfers are typically non periodic small device initiated communication requiring bounded latency such as a mouse or keyboard An Interrupt request is queued by the device until the host polls the USB device asking for data The maximum data payload size for low speed devices is 8 bytes for full speed devices is 64 bytes and for high speed devices 1024 bytes e Isochronous Transfers Isochronous transfers occur continuously and periodically They typically contain time sensitive information such as an audio or video stream If there were a delay or retry of data in an audio stream then you would expect some erratic audio containing glitches The beat may no longer be in sync However if a packet or frame was dropped every now and again it is less likely to be noticed by the listener Isochronous Transfers provide Guaranteed access to USB bandwidth Bounded latency e Stream Pipe Unidirectional e Error detection via CRC but no retry or guarantee of delivery e Full amp high speed modes only e No data toggling The maximum size data payload is specified in the endpoint descriptor of an Isochronous Endpoint This can be up to a maximum of 1023 bytes for a full speed device and 1024 bytes for a high speed device As the maximum data payload size is going to effect the bandwidth r
158. truments application software and required driver software on your embedded controller Summary PXI modular instrumentation defines a rugged computing platform for measurement and automation users that clearly takes advantage of the technology advancements of the mainstream PC industry By using the standard PCI bus PXI modular instrumentation systems can benefit from widely available software and hardware components The software applications and OSs that run on PXI systems are already familiar to users because they are already in use on common desktop computers PXI meets your needs by adding rugged industrial packaging plentiful slots for I O and features that provide advanced timing and triggering capabilities 4 USB An introduction to the USB bus Compiled from A USB Primer by Brian K Lewis Ph D Member of the Sarasota Personal Computer Users Group Inc USB in a nutshell by Craig Peacock and USB Complete Everything You Need to Develop Custom USB Peripherals by Jan Axelson Introduction The main reason for developing the Universal Serial Bus USB was to reduce the amount of cabling at the back of PCs Apple developed the Apple Desktop Bus with this intention where both the keyboard mouse and some other peripherals could be connected together daisy chained using one cable and this was the first development of the USB bus USB ports have a number of advantages over the old system of parallel serial ports
159. ts and configure them to generate interrupts or signals in a particular way For example a Commander can instruct its Servants to use a particular interrupt line to send signals rather than generate interrupts or configure the reporting of only certain status or error conditions Although the Word Serial Protocol is reserved for Commander Servant communications peer to peer communication between two VXI devices can be established through a specified shared memory protocol or by simply writing specific messages directly to the signal register of the device Slot 0 and the Resource Manager The leftmost slot of a VXI chassis has special system resources such as backplane clocks configuration signals and synchronization trigger signals and therefore must be occupied by a device with VXI Slot 0 capabilities The VXI Resource Manager RM function essentially a software module can reside on any VXI module or even on an external computer The RM in combination with the Slot O device identifies each device in the system assigns logical addresses memory configurations and establishes Commander Servant hierarchies using the Word Serial Protocol to grant Servants to the Commanders in the system After establishing the Commander Servant hierarchy the RM issues the Begin Normal Operation Word Serial command to all top level Commanders During normal system operation the RM may also halt the system and or remap the hierarchy 1f necessary Three
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161. u can build multichassis PXI systems with MXI 4 as well Using a MXI 4 link you can implement either a daisy chain or a star topology to build multichassis systems For more information on topologies for multichassis configurations refer to the MXI 4 Series User Manual You can purchase any desktop workstation or server computer and then remotely control your PXI system using either MXI Express or copper fiber optic MXI 4 serial link For more information please refer to PC control of PXI With PXI remote controllers you can maximize processor performance with minimized cost by using a desktop computer or laptop to remotely control a PXI system Because all remote control products are software transparent no additional programming is required PXI Embedded Controllers Embedded controllers eliminate the need for an external PC therefore providing a complete system contained in the PXI chassis PXI embedded controllers are typically built using standard PC components in a small PXI package For example the NI PXI 8187 controller has a Pentium 4 M 2 5 GHz processor up to 1 GB of DDR RAM a hard drive and standard PC peripherals such as USB 2 0 Ethernet serial and parallel ports Additionally you can install your choice of OSs on the PXI controller including Windows 2000 XP or LabVIEW Real Time yarns O A TRUMENTS y Rn 2 b I em o 24 TULLU x D HL Bink Ik het Figure 5 National
162. uch as Cypress Semiconductor also use a programmable resistor for Re Numeration purposes in their EZUSB devices where the one device can be enumerated for one function such as In field programming then be disconnected from the bus under firmware control and enumerate as another different device all without the user lifting an eyelid Many of the EzUSB devices do not have any Flash or OTP ROM to store code They are bootstraped at connection You will notice we have not included speed identification for High Speed mode High speed devices will start by connecting as a full speed device 1 5k to 3 3V Once it has been attached 1t will do a high speed chirp during reset and establish a high speed connection if the hub supports it If the device operates in high speed mode then the pull up resistor is removed to balance the line A USB 2 0 compliant device is not required to support high speed mode This allows cheaper devices to be produced if the speed isn t critical This is also the case for a low speed USB 1 1 devices which is not required to support full speed However a high speed device must not support low speed mode It should only support full speed mode needed to connect first then high speed mode if successfully negotiated later An USB 2 0 compliant downstream facing device Hub or Host must support all three modes high speed full speed and low speed USB Protocols Unlike RS 232 or similar serial interfaces where the format of data b
163. unctions GPIB Devices can be Talkers Listeners Types of GPIB Messages as initializing the bus addressing and and or Controllers A Talker sends data Sr GPIB devices communicate with other unaddressing devices and setting device messages to one or more Listeners which GPIB devices by sending device dependent modes for remote or local programming receive the data The Controller manages the messages and interface messages through flow of information on the GPIB by sending the interface system The term command as used here commands to all devices A digital voltmeter Device dependent messages often called should not be confused with some device for example is a Talker and is also a Listener data or data messages contain device instructions that are also called commands specific information such as programming Such device specific commands are actually The GPIB is like an ordinary computer bus instructions measurement results data messages as far as the GPIB interface except that a computer has its circuit cards machine status and data files system itself is concerned interconnected via a backplane the GPIB has stand alone devices interconnected by standard cables The role of the GPIB Controller is 8 Data Lines comparable to the role of a computer CPU but a better analogy is to compare the Controller to the switching center of a city telephone system Signal Lines A Handshaking Lines The switching center Co
164. undation will take the greater market share World Factory Instrumentation Protocol The World Factory Instrumentation Protocol WorldFIP was developed from an earlier French National Standard known as NFC 46 600 or more commonly as FIP It is a consortium of companies producing field bus instruments that use a messaging system Time critical options are supposedly guaranteed in a WorldFIP implementation WorldFIP plans to add a device description tool known as the WorldFIP Device Builder The Device Builder will automatically inform the control system what features and parameters each instrument connected to the bus has Interestingly WorldFIP is divisional in nature with a UK European and North American division Each division is motivated by similar goals and similar implementations but each operates almost autonomously from the others Some of the major members of WorldFIP include Honeywell Arizona Bailey Controls Ohio Cegelec Paris Allen Bradley Corporation Ohio Telemecanique Paris Ronan Engineering Co California Square D Electricite de France France Elf France Interoperable Systems Project The Interoperable Systems Project ISP implementation is based on the German National Standard DIN STD19245 also known as Process Field Bus or Profibus Profibus is similar to the token passing network commonly implemented on many networks today The ISP extension to Profibus is the Device Description Language
165. use and end user success In fact many of the largest instrument suppliers in the world are members of both organizations including National Instruments GenRad Hewlett Packard Racal Instruments and Tektronix With VXIplug amp play you are assured that components from different vendors will work reliably in the same system Members of the VXI Consortium and the VXIplug play Systems Alliance have combined their expertise to develop technically sound standards for both hardware and software bringing the entire industry into a new generation of instrumentation a generation that stresses ease of use and open systems without sacrificing flexibility or performance VXIbus Mechanical Configuration Physically a VXIbus system consists of a mainframe chassis that has the physical mounting and backplane connections for plug in modules as shown in Figure 1 The VXIbus uses the industry standard IEEE 1014 VMEbus as a base architecture to build upon As shown in Figure 2 VXI uses the full 32 bit VME architecture but adds two board sizes and one connector The P1 connector and the center row of the P2 connector are retained exactly as defined by the VME specification The VME user definable pins on the P2 connector and the additional pins on P3 the third VXI connector implement instrumentation signals between plug in modules directly on the backplane EA A Z Se F Figure 1 A VXIbus System The VXIbus specification includes packaging requ
166. ut a USB device could mean a USB transceiver device used at the host or peripheral a USB Hub or Host Controller IC device or a USB peripheral device The standard therefore makes references to USB functions which can be seen as USB devices which provide a capability or function such as a Printer Zip Drive Scanner Modem or other peripheral Bus Host USB Device LL LL Addrl Endpoint Direction My Function My Function Most functions will have a series of buffers typically 8 bytes long Each buffer will belong to what is referred to as an endpoint EPO IN EPO OUT etc see below Say for example the host sends a device descriptor request The function hardware will read the setup packet and determine from the address field whether the packet is for itself and if so will copy the payload of the following data packet to the appropriate endpoint buffer dictated by the value in the endpoint field of the setup token It will then send a handshake packet to acknowledge the reception of the byte and generate an internal interrupt within the semiconductor micro controller for the appropriate endpoint signifying it has received a packet This is typically all done in hardware The software now gets an interrupt and should read the contents of the endpoint buffer and parse the device descriptor request Endpoints Endpoints can be described as sources or sinks of data As the bus is host centric endpoints occur at the end of the com
167. y set or automatically configured by the system at startup is analogous to the GPIB address of a GPIB device Device Dependant Regita s YAI Config u aton peace Upper 16 EE of Alb space peered for Reserved by lla iz al conigurat on spa ce Speciosion B E pa device Ghrloocel address peces ba ze address Tor eech derc Communication Regsters 255 devices par WA eter 2 Required tor wil farsa ge Bed Demos Contgurton Reg ierz Required fr al Yal Devices Figure 3 VXI Configuration Registers Register Based Devices Because of the VXI configuration registers which are required for all VXI devices the system can identify each VXI device its type model and manufacturer address space and memory requirements VXIbus devices with only this minimum level of capability are called Register Based devices With this common set of configuration registers the centralized Resource Manager RM essentially a software module can perform automatic system and memory configuration when the system is initialized Message Based Communication In addition to Register Based devices the VXIbus specification also defines Message Based devices which are required to have communication registers and configuration registers All Message Based VXIbus devices regardless of the manufacturer can communicate at a minimum level using the VXI specified Word Serial Protocol When minimum communication is possible higher performance communication chan

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