ULTRA 485+2.PCI USER MANUAL
Contents
1. eee 13 MANUFACTURING 5 eere ECOLE POE REED Oe ee Gee Do Pase ARA 13 POWER CONSUMPTION visnet aie ii a 13 MEAN TIME BETWEEN FAILURES MTBF eee 13 PHYSICAL DIMENSIONG cssccssccessccessccesseccessccscecsecessccssscesseeecenees 13 APPENDIX A TROUBLESHOOTING cccccscscscscscscscscscscscscscee 14 PCI COM NUMBER SELECTION IN WINDOWS 95 15 APPENDIX B How TO GET ASSISTANCE e ecce cce ceeeeeess 16 APPENDIX C ELECTRICAL INTERFACE ee ecce ececeeeeeees 17 APPENDIX D ASYNCHRONOUS COMMUNICATIONS 18 APPENDIX E SILK SCREEN eee ecce eee senes es sssssssssssss 1D APPENDIX F COMPLIANCE NOTICES e esee eee eee sss 20 FEDERAL COMMUNICATIONS COMMISSION STATEMENT 20 EMC DIRECTIVE STATEMENT see ese esse ees ee ee ee ee ee ee ee 20 Figures Figure 1 Headers J1B and J2B RS 422 eese Be ee EER EE Re 3 Figure 2 Headers J1B and J2B RS 485 Auto Enabled with NO EChO 3 Figure 3 Headers J1B and J2B RS 485 Auto Enabled with ECHO T 3 Figure 4 Headers J1B and J2B RS 485 RTS Enabled with NO EChO 4 Figure 5 Headers J1B and J2B RS 485 RTS Enabled with De EI innir icti t nirin EEEN iA 4 Figure 6 Headers J1A2. SEALEVEL SYSTEMS INCORPORATED ULTRA 485 2 PCI USER MANUAL Part 7204 EE c Phone 864 843 4343 43 P O Box 830 FAX 864 843 3067 1 Liberty SC 29657 USA www sealevel com Contents OVERVIEW Ass E N t ehh OE GES thi ee thre 1 WHAT S INGEUDED ELE SEER Ee foo fre Coeds ette rot 1 FACTORY DEFAULT SETTINGS eere nennen nennen 1 CARD SETUP es ea cescvtoceuesencueaeeoeo cene ea oe se a cone ea cacao o ee RS 485 ENABLE MODES ees ee ees see ees ee ee ee ee ee ee ee ee Re ee Re Re ee ee 2 Interface Mode Examples J1B and J2B continued 4 ADDRESS AND IRQ SELECTION see see see see ee ee nnne nnn nnne 4 LINE TERMINATION ccsccessccessccesecessececsaccesecessccssecessecesseceaseceesseeaeeenee 5 COR MODES 5 5 OE EE OE 6 BAUD RATES AND DIVISORS FOR THE DIV1 MODE 7 BAUD RATES AND DIVISORS FOR THE DIV2 MODE eee 8 OPERATING SYSTEM INSTALLATION esse esse esse ene ee ee ee ee ee Re ee 9 For Windows Users esse esse ee ee ee ee ee ee ee ee ee ee ee 9 Other Operating Systems essere 9 SYSTEM INSTALLATION cech nne ethernet enne nennen 9 id ME de VR N ERR HERE EE GEE 10 WEYUSEANTSP EES ER ee ne ie E 11 CONNECTOR PIN ASSIGNMENTS eeue ees see ee ee ee ee ee ee ee ee Re ee 12 RS422 AE rne eR D Ne ERR EE EER 12 SPECIFICATIONS 5rd tito Od eot iet Reni ENVIRONMENTAL SPECIFICATIONS
3. for any claim made by any other related party RETURN AUTHORIZATION MUST BE OBTAINED FROM SEALEVEL SYSTEMS BEFORE RETURNED MERCHANDISE WILL BE ACCEPTED AUTHORIZATION CAN BE OBTAINED BY CALLING SEALEVEL SYSTEMS AND REQUESTING A RETURN MERCHANDISE AUTHORIZATION RMA NUMBER Sealevel Systems Incorporated 155 Technology Place P O Box 830 Liberty SC 29657 USA 864 843 4343 FAX 864 843 3067 www sealevel com email support sealevel com Technical Support is available from 8 a m to 5 p m Eastern time Monday Friday Trademarks Sealevel Systems Incorporated acknowledges that all trademarks referenced in this manual are the service mark trademark or registered trademark of the respective company ULTRA 48542 PCI is a trademark of Sealevel Systems Incorporated Sealevel Systems ULTRA 485 2 PCI Page 21
4. RB R8 R9 R10 R11 LL LL pur R12U3 75174 m R13 PORT J2 PPTLL i re U7 16550 PLCC U9 iA PLCC U2 GD75232 m R14 U4 75175 R27 C15 PPTLL R15 R28 RE OMGE BY T y R19 R23 DIv2 DMDE BY 2 p HEADER24PINW E3 cB PCIgese DM4 DMDE BY 4 N PORTI J1 5 us a3cs4q PORT2 zx i HEADER24PINW E4 COPYRIGHT 1997 cB MADE IN USA a e pony T TERMINATION ENABLE C 4 L CONNECT RX TO TX P1 4 2 Page 19 Sealevel Systems ULTRA 485 2 PCI Appendix F Compliance Notices Appendix F Compliance Notices Federal Communications Commission Statement FCC This equipment has been tested and found to comply with the limits for Class A digital device pursuant to Part 15 of the FCC Rules These limits are designed to provide reasonable protection against harmful interference when the equipment is operated in a commercial environment This equipment generates uses and can radiate radio frequency energy and if not installed and used in accordance with the instruction manual may cause harmful interference to radio communications Operation of this equipment in a residential area is likely to cause harmful interference in such case the user will be required to correct the interference at his own expense EMC Directive Statement Products bearing the CE Label fulfill the requirements of the EMC directive 89 336 EEC and of the low voltage directive 73 23 EEC issued by the European Commission To obey these directives the f
5. of the interrupt The software designer frequently used a technique referred to as round robin polling This method required the interrupt service routine to poll or interrogate each UART as to its interrupt pending status This method of polling was sufficient for use with slower speed communications but as modems increased their through put abilities this method of servicing shared IRQs became inefficient Sealevel Systems ULTRA 485 2 PCI Page 10 Technical Description Why use an ISP The answer to the polling inefficiency was the Interrupt Status Port ISP The ISP is a read only 8 bit register that sets a corresponding bit when an interrupt is pending Port 1 interrupt line corresponds with Bit DO of the status port Port 2 with D1 etc The use of this port means that the software designer now only has to poll a single port to determine if an interrupt is pending The ISP is at Base 7 on each port Example Base 280 Hex Status Port 287 28F etc The ULTRA 485 2 PCI will allow any one of the available locations to be read to obtain the value in the status register Both status ports on the ULTRA 485 2 PCI are identical so any one can be read Example This indicates that Channel 2 has an interrupt pending HER 2 1 Jo o o To fo a l0 Bit Position 7 6 Value Read 0 0 Sealevel Systems ULTRA 485 2 PCI Page 11 Technical Description Connector Pin Assignments RS 422 485 GND Ground
6. to use Refer to the README file on the supplied diskette for detailed instructions on using SSD For Windows 95 and Windows NT the diagnostic tool WinSSD is installed in the Sealevel folder on the Start Menu during the setup process First find the ports using the Device Manager then use WinSSD to verify that the ports are functional Always use the Sealevel Systems diagnostic software when troubleshooting a problem This will eliminate any software issues from the equation Sealevel Systems ULTRA 485 2 PCI Page 14 Appendix A Troubleshooting PCI COM NUMBER SELECTION IN WINDOWS 95 When installing a multi port PCI card in Windows 95 the default starting COM number assigned to the first port will be COM 5 if no COM 5 exists If there is a COM 5 6 etc the next available COM number will be assigned to the first port with all additional ports following in ascending order To change the first two ports so that Windows assigns them COM 3 and COM 4 port enumeration double click the Systems icon in control panel or right click on My Computer and choose properties which will bring you to System Properties Choose the Device Manager tab and double click on the Multi Function Adapter heading This will show all the information concerning the Sealevel adapter Choose the Resources tab which will show all resources assigned to the multi function adapter Uncheck the Use Automatic Settings box Notice that with a two port
7. 5 Transmit Data Positive 4 Output Transmit Data Negative 3 Output Request To Send Positive 6 Output Request To Send Negative 7 Output Receive Data Positive 1 Input RX RX Receive Data Negative 2 Input CTS Clear To Send Positive 9 Input CIS Clear To Send Negative 8 Ipt Technical Note Please terminate any control signals that are not going to be used The most common way to do this is connect RTS to CTS and RTS to CTS Terminating these pins if not used will help insure you get the best performance from your adapter Sealevel Systems ULTRA 485 2 PCI Page 12 Specifications Specifications Environmental Specifications Temperature Range 0 to 50 C 20 to 70 C 32 to 122 F 4 to 158 F Humidity Range 10 to 90 R H 10 to 90 R H Non Condensing Non Condensing Manufacturing e All Sealevel Systems Printed Circuit boards are built to U L 94V0 rating and are 100 electrically tested These printed circuit boards are solder mask over bare copper or solder mask over tin nickel Power Consumption Supply line 12VDC 12VDC 5 VDC 480 mA Mean Time Between Failures MTBF Greater than 150 000 hours Calculated Physical Dimensions Board length 5 0 inches 12 7 cm Board Height including Goldfingers 4 2 inches 10 66 cm Board Height excluding Goldfingers 3 875 inches 9 841 cm Sealevel Systems ULTRA 485 2 PCI Page 13 Appendix A Troubleshooti
8. S 485 mode our special auto enable feature allows the RS 485 ports to be viewed by the operating system as a COM port This allows the standard COM driver to be utilized for RS 485 communications Our on board hardware automatically handles the RS 485 driver enable What s Included The ULTRA 485 2 PCI is shipped with the following items If any of these items are missing or damaged contact the supplier e ULTRA 485 2 PCI Serial VO Adapter e Serial Utility Software e User Manual Factory Default Settings The ULTRA 485 2 PCI factory default settings are as follows Port Electrical Specification Port 1 RS 422 RS 422 To install the ULTRA 485 2 PCI using factory default settings refer to Installation on page 9 For your reference record installed ULTRA 485 2 PCI settings below Port Electrical Specification Port 1 Po Port Sealevel Systems ULTRA 485 2 PCI Page 1 Card Setup Card Setup In all cases J1x refers to settings for the first port and J2x refer to settings for the second port RS 485 Enable Modes RS 485 is ideal for multi drop or network environments RS 485 requires a tri state driver that will allow the electrical presence of the driver to be removed from the line The driver is in a tri state or high impedance condition when this occurs Only one driver may be active at a time and the other driver s must be tri stated The output modem control signal Request To Send RTS is typically us
9. and J2A Line Termination 5 Figure 7 Clocking Mode Divide By 4 se ee EE Ee Ge ese 6 Figure 8 Clocking Mode Divide By 2 eere eee estet eee ee 6 Figure 9 Clocking Mode Divide By 1 ee Se Se EE ee Ee ese 6 Figure 10 Asynchronous Communications Bit Diagram 18 2002g Sealevel Systems Incorporated All rights reserved Introduction Introduction Overview The Sealevel Systems ULTRA 485 2 PCI is a two channel PCI Bus serial I O adapter for the PC and compatibles and features the 16850 advanced UART It provides two field selectable RS 422 485 serial ports supporting data rates up to 460 8K bps The 16850 advanced UART provides a 128 byte FIFO that helps reduce processor overhead by reducing the number of interrupts that need servicing Each port can be individually configured Choose the RS 422 mode for long distance device connections up to 4000ft where noise immunity and high data integrity are essential Select RS 485 and capture data from multiple peripherals in a RS 485 multidrop network Up to 31 RS 485 devices can be connected to each port to automate your data collection You can even mix the ports in any of the interface combinations to provide maximum flexibility to your application In RS 422 mode the card works seamlessly with the standard operating system serial driver In R
10. and its importance to the IBM PC can be found in the book Peter Norton s Inside the PC Premier Edition A good analogy of a PC interrupt would be the phone ringing The phone bell is a request for us to stop what we are currently doing and take up another task speak to the person on the other end of the line This is the same process the PC uses to alert the CPU that a task must be preformed The CPU upon receiving an interrupt makes a record of what the processor was doing at the time and stores this information on the stack this allows the processor to resume its predefined duties after the interrupt is handled exactly where it left off Every main sub system in the PC has it s own interrupt frequently called an IRQ short for Interrupt ReQuest The following IRQ table will define the system IRQs as well as show typically free IRQs In these early days of PC s Sealevel Systems decided that the ability to share IRQs was an important feature for any add in I O card Consider that in the IBM XT the available IRQs were IRQO through IRQ7 Of these interrupts only IRQ2 5 and IRQ7 were actually available for use This made the IRQ a very valuable system resource To make the maximum use of these system resources Sealevel Systems devised an IRQ sharing circuit that allowed more than one port to use a selected IRQ This worked fine as a hardware solution but presented the software designer with a challenge to identify the source
11. at http www sealevel com faq htm 4 Visit Sealevel s website at www sealevel com for the latest software updates and newest manuals 5 Technical support is available Monday to Friday from 8 00 a m to 5 00 p m eastern time Technical support can be reached at 864 843 4343 RETURN AUTHORIZATION MUST BE OBTAINED FROM SEALEVEL SYSTEMS BEFORE RETURNED MERCHANDISE WILL BE ACCEPTED AUTHORIZATION CAN BE OBTAINED BY CALLING SEALEVEL SYSTEMS AND REQUESTING A RETURN MERCHANDISE AUTHORIZATION RMA NUMBER Sealevel Systems ULTRA 485 2 PCI Page 16 Appendix C Electrical Interface Appendix C Electrical Interface RS 422 The RS 422 specification defines the electrical characteristics of balanced voltage digital interface circuits RS 422 is a differential interface that defines voltage levels and driver receiver electrical specifications On a differential interface logic levels are defined by the difference in voltage between a pair of outputs or inputs In contrast a single ended interface for example RS 232 defines the logic levels as the difference in voltage between a single signal and a common ground connection Differential interfaces are typically more immune to noise or voltage spikes that may occur on the communication lines Differential interfaces also have greater drive capabilities that allow for longer cable lengths RS 422 is rated up to 10 Megabits per second and can have cabling 4000 feet long RS 422 also define
12. card there will be three input output I O ranges listed With a four port card there will be five input output I O ranges listed The first I O range is for the PCI bus and should not be changed The second and third I O ranges are the ones that need to be changed in order to have those ports enumerated as COM 3 and COM 4 Double click on the second I O range which will allow you to change the address Highlight the entire I O range and type 03e8 03ef for COM 3 Click OK Windows will inform you that you have made modifications that may affect other devices Click OK Next double click on the third I O range Highlight the entire I O range and type 02e8 02ef for COM 4 Again Windows will inform you that you have made modifications that may affect other devices Click OK Following these steps will change the COM number assignments on the first two ports to COM 3 and 4 Sealevel Systems ULTRA 485 2 PCI Page 15 Appendix B How To Get Assistance Appendix B How To Get Assistance 1 Begin by reading through the Trouble Shooting Guide in Appendix A If assistance is still needed please see below 2 When calling for technical assistance please have your user manual and current adapter settings If possible please have the adapter installed in a computer ready to run diagnostics 3 Sealevel Systems provides an FAQ section on its web site Please refer to this for many commonly asked questions This section can be found
13. ed to control the state of the driver Some communication software packages refer to RS 485 as RTS enable or RTS block mode transfer One of the unique features of the ULTRA 485 2 PCI is the ability to be RS 485 compatible without the need for special software or drivers This ability is especially useful in Windows Windows NT and OS 2 environments where the lower level I O control is abstracted from the application program This ability means that the user can effectively use the ULTRA 485 2 PCI in a RS 485 application with existing i e standard RS 232 software drivers Headers JIB and J2B are used to control the RS 485 mode functions for the driver circuit The selections are RTS enable silk screen RT or Auto enable silk screen AT The Auto enable feature automatically enables disables the RS 485 interface The RTS mode uses the RTS modem control signal to enable the RS 485 interface and provides backward compatibility with existing software products Position 3 silk screen NE of JIB and J2B is used to control the RS 485 enable disable functions for the receiver circuit and determine the state of the RS 422 485 driver The RS 485 Echo is the result of connecting the receiver inputs to the transmitter outputs Every time a character is transmitted it is also received This can be beneficial if the software can handle echoing i e using received characters to throttle the transmitter
14. ng Appendix A Troubleshooting A Serial Utility Diskette is supplied with the Sealevel Systems adapter and will be used in the troubleshooting procedures By using this diskette and following these simple steps most common problems can be eliminated without the need to call Technical Support 1 Identify all I O adapters currently installed in your system This includes your on board serial ports controller cards sound cards etc The I O addresses used by these adapters as well as the IRQ if any should be identified Configure your Sealevel Systems adapter so that there is no conflict with currently installed adapters No two adapters can occupy the same I O address Make sure the Sealevel Systems adapter is using a unique IRQ While the Sealevel Systems adapter does allow the sharing of IRQs many other adapters i e SCSI adapters amp on board serial ports do not The IRQ is typically selected via an on board header block Refer to the section on Card Setup for help in choosing an I O address and IRQ Make sure the Sealevel Systems adapter is securely installed in a motherboard slot When running DOS or Windows 3 x refer to the Serial Utilities disk 1 and the User Manual to verify that the Sealevel Systems adapter is configured correctly The supplied diskette contains a diagnostic program SSD that will verify if an adapter is configured properly This diagnostic program is written with the user in mind and is easy
15. ohm pull up pull down combination that biases the receiver inputs Headers J1A and J2A allow the user to customize this interface to their specific requirements Each jumper position corresponds to a specific portion of the interface If multiple ULTRA 485 2 PCI adapters are configured in a RS 485 network only the boards on each end should have jumpers T P amp P ON Refer to the following table for each position s operation Function Adds or removes the IK ohm pull down resistor in the RS 422 RS 485 receiver circuit Receive data only Adds or removes the IK ohm pull up resistor in the RS 422 RS 485 receiver circuit Receive data only Adds or removes the 120 ohm termination Connects the TX to RX for RS 485 two wire operation Connects the TX to RX for RS 485 two wire operation IN P Pd dd Figure 6 Headers JIA and J2A Line Termination Sealevel Systems ULTRA 485 2 PCI Page 5 Card Setup Clock Modes The ULTRA 485 2 PCI employs a unique clocking option that allows the end user to select from divide by 4 divide by 2 and divide by 1 clocking modes These modes are selected at Headers J1C through JAC To select the Baud rates commonly associated with COM ports i e 2400 4800 9600 19 2 115 2K Bps place the jumper in the divide by 4 mode silk screen DIV4 DIV2 0 O og DIVANNN DIV Figure 7 Clocking Mode Divide By 4 To double these rates up to a maximum rate f
16. ollowing European standards must be met ENS5022 Class A Limits and methods of measurement of radio interference characteristics of information technology equipment ENS5024 Information technology equipment Immunity characteristics Limits and methods of measurement EN60950 IEC950 Safety of information technology equipment including electrical business equipment Warning This is a Class A Product In a domestic environment this product may cause radio interference in which case the user may be required to take adequate measures Always use cabling provided with this product if possible If no cable is provided or if an alternate cable is required use high quality shielded cabling to maintain compliance with FCC EMC directives Sealevel Systems ULTRA 485 2 PCI Page 20 Warranty Warranty Sealevel Systems Inc provides a limited lifetime VAFETIMe warranty Should this product fail to be in good working order at any time during this period Sealevel Systems will at it s option replace or repair it at no additional charge except as set forth in the following terms This warranty does not apply to products damaged by misuse modifications accident or disaster Sealevel Systems assumes no liability for any damages lost profits lost savings or any other incidental or consequential damage resulting from the use misuse of or inability to use this product Sealevel Systems will not be liable
17. or 230 4K bps place the jumper in the divide by 2 silk screen DIV2 position Og sd Og DIV DIV2 DIV4 Figure 8 Clocking Mode Divide By 2 To select the maximum data rate 460 8K bps place the jumper in the divide by 1 silk screen DIV1 position a Dna 4n DIV DIV2 DIV Figure 9 Clocking Mode Divide By 1 Sealevel Systems ULTRA 485 2 PCI Page 6 Card Setup Baud Rates and Divisors for the Divl mode The following table shows some common data rates and the rates you should choose to match them if using the adapter in the Div1 mode 2400 bps 600 bps 9600 bps 2400 bps 57 6 K bps 14 4K bps 230 4K bps 57 6 K bps If your communications package allows the use of Baud rate divisors choose the appropriate divisor from the following table For this Data Rate Choose this Divisor 1200 bps 384 9600 bps 48 19 2K bps 24 38 4K bps 1 57 6K bps 460 8K bps Sealevel Systems ULTRA 485 2 PCI Page 7 Card Setup Baud Rates and Divisors for the Div2 mode The following table shows some common data rates and the rates you should choose to match them if using the adapter in the Div2 mode 2400 bps 1200 bps 9600 bps 4800 bps 38 4K bps 19 2K bps 57 6 K bps 28 8K bps 115 2 K bps 57 6 K bps 230 4 K bps 115 2 K bps If your communications package allows the use of Baud rate divisors choose the appropriate divisor from the following table 1200 bp
18. or it can confuse the system if the software does not To select the No Echo mode select silk screen position NE For RS 422 compatibility remove the jumpers at JIB and J2B Examples on the following pages describe all of the valid settings for JIB and J2B Sealevel Systems ULTRA 485 2 PCI Page 2 Card Setup Interface Mode Examples J1B J2B EE 4n NE Figure 1 Headers JIB and J2B RS 422 E OO pn RT NE E lt Figure 2 Headers J1B and J2B RS 485 Auto Enabled with No Echo E Eeg 4 uz Figure 3 Headers JIB and J2B RS 485 Auto Enabled with Echo Sealevel Systems ULTRA 485 2 PCI Page 3 Card Setup Interface Mode Examples J1B and J2B continued N o ee 4 uz Figure 4 Headers JIB and J2B RS 485 RTS Enabled with No Echo cE ee 4 uz Figure 5 Headers J1B and J2B RS 485 RTS Enabled with Echo Address and IRQ selection The ULTRA 485 2 PCI is automatically assigned I O addresses and IRQs by your motherboard BIOS Only the I O address may be modified by the user Adding or removing other hardware may change the assignment of I O addresses and IRQs Sealevel Systems ULTRA 485 2 PCI Page 4 Card Setup Line Termination Typically each end of the RS 485 bus must have line terminating resistors RS 422 terminates at the receive end only A 120 ohm resistor is across each RS 422 485 input in addition to a 1K
19. s 192 4800 bps 19 2K bps 57 6K bps 115 2K bps 230 4K bps Sealevel Systems ULTRA 485 2 PCI Page 8 Installation Installation Operating System Installation For Windows Users Start by choosing Install Software at the beginning of the CD Choose Asynchronous COM Port Software SeaCOM Other Operating Systems Refer to the appropriate section of the Serial Utilities Software System Installation System Installation The ULTRA 485 2 PCI can be installed in any of the PCI expansion slots and contains several jumper straps for each port that must be set for proper operation Turn off PC power Disconnect the power cord Remove the PC case cover Locate an available PCI slot and remove the blank metal slot cover Gently insert the ULTRA 485 2 PCI into the slot Make sure that the adapter is seated properly 5 Replace the screw 6 Replace the cover 7 Connect the power cord BRWN Re Installation is complete Sealevel Systems ULTRA 485 2 PCI Page 9 Technical Description Technical Description The Sealevel Systems ULTRA 485 2 PCI provides a PCI interface adapter with 2 asynchronous field selectable RS 422 485 serial ports for industrial automation and control applications The ULTRA 485 2 PCI uses the 16850 advanced UART This chip features programmable baud sates data format interrupt control and a 128 byte input and output FIFO Interrupts A good description of an interrupt
20. s driver and receiver electrical characteristics that will allow 1 driver and up to 32 receivers on the line at once RS 422 signal levels range from 0 to 5 volts RS 422 does not define a physical connector RS 485 RS 485 is backwardly compatible with RS 422 however it is optimized for partyline or multi drop applications The output of the RS 422 485 driver is capable of being Active enabled or Tri State disabled This capability allows multiple ports to be connected in a multi drop bus and selectively polled RS 485 allows cable lengths up to 4000 feet and data rates up to 10 Megabits per second The signal levels for RS 485 are the same as those defined by RS 422 RS 485 has electrical characteristics that allow for 32 drivers and 32 receivers to be connected to one line This interface is ideal for multi drop or network environments RS 485 tri state driver not dual state will allow the electrical presence of the driver to be removed from the line Only one driver may be active at a time and the other driver s must be tri stated RS 485 can be cabled in two ways two wire and four wire mode Two wire mode does not allow for full duplex communication and requires that data be transferred in only one direction at a time For half duplex operation the two transmit pins should be connected to the two receive pins Tx to Rx and Tx to Rx Four wire mode allows full duplex data transfers RS 485 does not define a connector pin out or a
21. set of modem control signals RS 485 does not define a physical connector Sealevel Systems ULTRA 485 2 PCI Page 17 Appendix D Asynchronous Communications Appendix D Asynchronous Communications Serial data communications implies that individual bits of a character are transmitted consecutively to a receiver that assembles the bits back into a character Data rate error checking handshaking and character framing start stop bits are pre defined and must correspond at both the transmitting and receiving ends Asynchronous communications is the standard means of serial data communication for PC compatibles and PS 2 computers The original PC was equipped with a communication or COM port that was designed around an 8250 Universal Asynchronous Receiver Transmitter UART This device allows asynchronous serial data to be transferred through a simple and straightforward programming interface A start bit followed by a pre defined number of data bits 5 6 7 or 8 defines character boundaries for asynchronous communications The end of the character is defined by the transmission of a pre defined number of stop bits usually 1 1 5 or 2 An extra bit used for error detection is often appended before the stop bits Idle state of Odd Even line J4 5 to 8 Data Bits el Unused Vice n i i quc c quem er SP du 0 sdeccectodesbebcds bod i Jw 3I ret ogg RM 1 5 94 ke 2 Figure 10 A
22. synchronous Communications Bit Diagram This special bit is called the parity bit Parity is a simple method of determining if a data bit has been lost or corrupted during transmission There are several methods for implementing a parity check to guard against data corruption Common methods are called E ven Parity or O dd Parity Sometimes parity is not used to detect errors on the data stream This is refereed to as N o parity Because each bit in asynchronous communications is sent consecutively it is easy to generalize asynchronous communications by stating that each character is wrapped framed by pre defined bits to mark the beginning and end of the serial transmission of the character The data rate and communication parameters for asynchronous communications have to be the same at both the transmitting and receiving ends The communication parameters are baud rate parity number of data bits per character and stop bits i e 9600 N 8 1 Sealevel Systems ULTRA 485 2 PCI Page 18 Appendix E Silk Screen Appendix E ilk creen 7201 c1 R1 R2 Ul pp75232 c2 C4 5 0 JXB JUNPER SETTINGS Ue Y1 RS422 REMDVE ALL JUMPERS RS485 AT AUTO ENABLE c10 RS485 RT RTS ENABLE R5485 NE NO ECHO LODS s 25 c5 N HEADER24PINW Jer a1 ERA EI C14 E XC9536 7201 x Z RIG R20 R24 PORT 1 Sones A R17 R21 R25 N HEADER24PINW go HEADER24PINW JE Ria R22 RIG E5 ES C3 R4
Download Pdf Manuals
Related Search