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1. bits Parity is used to detect errors caused by noise in data transmission PC Personal Computer coined by IBM when it introduced its first IBM PC Jr which later became PC XT AT 286 386 486 Pentium Pro MMX Pentium and latest Pentium II Peer to Peer Two devices that can talk to each other Both devices can initiate communications This may also be called Master to Master communications Profibus Profibus is actually three buses Profibus FMS Field Message Specification Profibus PA Process Automation and Profibus DP Process Periphery FMS is a higher level bus intended to operate with PLCs Pcs and higher level nodes Profibus DP supports three masters The masters then operate with field nodes as master to slaves Profibus PA is an intrinsically safe bus The protocol is essentially the same as DP but the electrical physical specifications are modified to satisfy low voltage and current requirements Protocol A set of rules for communication This will specify what method to transfer information packet size information headers and who should talk when It is used to coordinate communication activity Receive To accept data sent from another device The device that receives the data is the receiver Register An area of memory that provides temporary storage of digital data RJ11 A connector used on most telephones that has four terminals SDS Smart Distributed System is a CAN based2. A local area network developed by Xerox in the early 70 s and standardized by Xerox Digital Equipment and Intel in 1978 This is a serial communications method which all devices share the lines An address is sent in a packet to talk to a device on the line This protocol supports peer to peer communications Even This term is used with parity See parity Fieldbus The term fieldbus is a general definition for an industrial network media that resides at the machine level and below ina total network system The primary purpose of this network is to interconnect the machine level and sublevel control functions and services in a distributive topology It is not a particular protocol or physical connection system Included in this generalization definition are standard protocols of Profibus Modbus DeviceNet SDS WorldPIP and P Net Firmware Instruction or data stored in an IC integrated circuit or on a read only disk Watlow Controls Communications Guide 25 This data is programmed once and cannot easily be changed as software can Full See Full Duplex Full Duplex Full is used to mean the duplex s full capability The ability to send and receive data at the same time The same as duplex GPIB See IEEE488 Half Duplex The ability to send or receive data but not at the same time To listen or talk but not both at the same time Handshake Handshaking Exchange of predetermined signals between t
3. 6o om Aa 2 25 2 5 2 11 Aa 2 2 2 2 2 1 1 c CON Oo OB cof pot O co Cc pn co 9 A B NUL S0H SIX ETX IRE TN ENQ PACK HE CR S0 Hoe DCI DC2 DOS DC4 NAK SYN ETB EM SUB ESC FS SP aaa Es S x2 ne EE E per Higgs Io NN reet 6 erel 9 9 pm OYOWowo yor ooo oo Si BIB 4 BiB 4 BIB BY Cop Co Co Cop Co Co Cop Co Co co n5 DSP POPPY nS n nS nS MS POY 2 gt gt gt 4 11 I sl a cl ce ojojo co oo 1 o o1 BI 25 IRS Ea OC CO Cof Ni Op Ca BJ Cop n5 CO Ke Oo Ny nf BI Coppa O co oo NID OF BI Colpo f e Ke kes kl kex Ca eS DS Gm OI C1 fas Xe Watlow Controls Communications Guide 6 Serial Communication The interfaces we ve chosen employ serial communication which is the exchange of data in a one bit at a time sequential manner on a single data line or channel Serial contrasts with parallel communication which sends several bits of information simultaneously over multiple lines or channels Not only is serial data communication simpler than parallel it is also less costly ASCII Control Codes ASCII Control Codes are used to give instructions to the remote device and result in specific actions such as a line feed instruction on a printer ASCII Control Codes the first
4. device level control network that can be scan or event driven configured as master slave or peer to peer and can support devices of varying complexity Uses twisted pair wires for the power and bus Slave A device that only responds to commands This device never starts communication on it s own Only the Master can do this See Master SCADA Supervisory Control and Data Acquisition Serial To process something in order First item second item etc Serial Communications A method of transmitting information between devices by sending all bits serially see serial over a single communication channel EIA TIA 232 Formerly RS 232 An Electronic Industries Association EIA Telecommunication Industry Association TIA standard for interface Watlow Controls Communications Guide 27 between data terminal equipment and data communications equipment for serial binary data interchange This is usually for communications over a short distance 50 feet or less and to a single device EIA TIA 485 Formerly RS 485 An Electronic Industries Association EIA Telecommunication Industry Association TIA standard for electrical characteristics of generators and receivers for use in balanced digital multi point systems This is usually used to communicate with multiple devices over a common cable or where distances over 50 feet are required Software Information of data or program stored in an easily changea
5. 06 00 07 2E EO 24 23 Received 01 86 03 02 61 Special Modbus Functions The following are Modbus registers with special functions 24 Disable Non volatile system Memory 106 Alarm Status Output 2 110 Alarm Status Output 3 114 Alarm Status Output 4 200 Auto Manual Operation Mode 311 Clear Input Errors 331 Clear Alarms 332 Silence Alarms A 0 indicates an inactive state Send 1 to the register to activate the function It will automatically reset to 0 when the function is complete See your User s Manual for detail on your specific model Watlow Controls Communications Guide 17 Handling Error Codes Error codes are divided into two types Read error codes and write error codes are called exception codes Reading from a register that does not exist or is currently disabled will typically respond with a large out of range value such as 32000 32001 or 32002 The Series 988 returns a value of zero Writing to a register that is not supported is inactive or out of range will return a packet with 0x80 added to the command sent The byte following this will contain the value 0x01 for illegal command 0x02 for illegal address or 0x03 for illegal data value Writing to a read only register will return an exception code 0x02 See your user s manual for exact values and definitions User Responsibility Users must refrain from altering prompts that do not appear on the controller s front panel o
6. 33 ASCII characters non printable are important for the operation of communicating equipment They give instruction to remote devices that result in specific actions such as a line feed on a printer Holding down the keyboard control key while pressing the appropriate keyboard key will send these values EMI ARE RN n Char Equiv Char Equiv NUL 00 00 Crti NullCharacter DCt 17 11 CrlQ Data Control 1 XON ACK 06 06 CrtiF Acknowledge ETB 23 17 Crl W Endof Trans Block BEL 07 07 CriG Bell CAN 24 18 CX Cancel BS 08 08 CrlH BackSpace EM 25 19 Cr Y End of Medium HT o9 09 Cr l Horizontal Tabulation SUB 26 1A CrilZ Substitute VT 11 OB Cr K Vertical Tabulation FS 28 1C Crti File Separator CR 13 OD Crl M CariageRetum RS 30 1E Crtl Record Separator Shift In SP 32 20 Space Data Link Escape 1 Parity Bit Remember that ASCII is a seven or eight bit code What about that eighth bit It s called the parity bit A parity bit is added to the ASCII character to verify the accuracy of the first seven bits We are declaring that the number of 1s in the 8 bit character frame will be either always odd or always even This way we can detect a single error in the seven bit group Take a look at the representation of the transmitted upper case W In this c
7. ANSI x3 28 and XON XOFF protocols Comm4 Diagnostic Software The COMMA EXE program can be downloaded free of charge from our BBS at 507 452 3958 This is a terminal program which handles the protocol for you The program can be used to determine if your cables are properly connected and that the controller is working This program supports the ANSI x3 28 and XON XOFF protocols CommsSwvb Diagnostic Software The COMMSVB EXE program can be downloaded free of charge from our BBS at 507 452 3958 This is a terminal program that handles the protocol for you The program can be used to determine if your cables are properly connected and that the controller is working This program supports the Modbus ANSI x3 28 and XON XOFF protocols CRC Cyclical Redundancy Checksum CRC Algorithm This C routine calc crc calculates the cyclical redundancy checksum CRC for a string of characters The CRC is the result of dividing the string by 0xA001 Modbus applications calculate the packet s CRC then append it to the packet Watlow Controls Communications Guide define POLYNOMIAL 0xA001 unsigned int calc crc unsigned char start of packet unsigned char end of packet unsigned int crc unsigned char bit count unsigned char char ptr Start at the beginning of the packet char ptr start of packet Initialize CRC crc Oxffff Loop through the entire packet do Exclusive OR the byte
8. This is the simplest protocol offered by Watlow Controls ANSI x3 28 The second called Full Protocol is based on the American National Standard Institute s standard ANSI X3 28 1976 Subcategory 2 2 The Full Protocol is required for systems that need a response to every message and for any multi drop network which has more than two communication devices Addressing a certain controller on the bus then enclosing all messages with a lt STX gt start of text 0x02 and lt ETX gt end of text 0x03 controls information exchange The characters lt ENQ gt lt EOT gt lt DLE gt are used to determine who has control of the bus Lastly all messages are lt ACK gt Watlow Controls Communications Guide 11 acknowledged 0x06 or lt NAK gt negative acknowledged 0x15 to ensure messages where received correctly Modbus Remote Terminal Unit RTU Gould Modicon now called AEG Schneider created the third protocol for process control systems called Modbus This protocol is the most complex of the three It has the advantage of being extremely reliable in exchanging information a highly desirable feature for industrial data communications This protocol works on the principle of packet exchanges The packet contains the address of the controller to receive the information a command field that says what is to be done with the information and several fields of data Reading from these registers retrieves all info
9. dam age resulting from transportation alteration misuse or abuse Returns Call or fax Customer Service for a Return Material Authorization RMA number before returning a controller e Put the RMA number on the shipping label and also on a written descrip tion of the problem A restocking charge of 2096 of the net priceis charged for all standard units returned to stock Watlow Controls Communications Guide Watlow Controls 1241 Bundy Blvd P O Box 5580 Winona Minnesota USA 55987 5580 Phone 507 454 5300 Fax 507 452 4507
10. different data communications protocols just as there are different human cultural protocols that vary according to the situation The protocol part of Watlow communications is very important because it gives us a quality of communication that others often don t have Protocol driven communications are more accurate because they are less prone to both operator and noise errors Protocol maintains system integrity by requiring a response to each message It s like registered mail you know that your letter has been received because the post office sends you a signed receipt In Watlow data communications a dialog will continue successfully as long as the messages are in the correct form and responses are returned to the protocol leader If the operator enters an incorrect message or interference comes on to the data line there will be no response In that case the master must retransmit the message or go to a recovery procedure If an operator continues to enter an incorrect message or interference continues on the data line the system will halt until the problem is resolved Watlow provides you with three protocol choices XON XOFF ANSI x3 28 Modbus RTU XON XOFF The first protocol is conventional XON XOFF protocol It works very well for systems that do not require a message response and for those with only two devices one PC and one controller Sending of the XON 0x11 and XOFF 0x13 controls information
11. error 0x02 See Exception Responses pg 4 9 Packet sent to controller nn 06 nnnn nnmn nnmn A AA A A A controller address one byte write to a register command 0x06 register high byte register low byte data high byte data low byte CRC low byte CRC high byte Example 988 only Set register 7 SPI to 200 0x00C8 on controller at address 9 Sent 09 06 00 07 00 C8 38 D5 Received 09 06 00 07 00 C8 38 D5 Write to Multiple Registers Command 0x10 This command actually writes a parameter to only a single register An attempt to write to a read only parameter returns an illegal data address error 0x02 See Exception Responses pg 4 9 Packet sent to controller nn 10 nnnn 0001 02 nnnn nnnn A A A AA A A AA A controller address one byte J write to multiple registers command 0x10 starting register high byte starting register low byte number of registers to write high byte 0x00 number of registers to write low byte must be 0x01 number of data bytes must be 0x02 data high byte data low byte CRC low byte CRC high byte Watlow Controls Communications Guide 15 Packet returned by controller nn 10 nnnn 0001 nnnn A A A A controller address one byte write to multiple registers command starting register high byte starting register low byte number of registers to write high byte 0x00
12. for each letter digit and punctuation mark ASCII also includes control characters similar to those we find on computer keys such as backspace shift and return It also has nine communications control characters for identification enquiry inquiry start of text end of text end of transmission acknowledge negative acknowledge and escape The ASCII code is sometimes written in a base 16 number system that is called hexadecimal or hex for short The numbers 0 through 9 represents the first ten digits of this system and the letters A through F represents the final six digits The 128 ASCII character code with the decimal and hexadecimal equivalents is listed below ASCII Chart No Parity 7 bit w Even 7 bit w Odd No Parity Thitw Even 7bitw Odd 7 or 8 bit Parity Parity 7 or 8 bit Parity Parity NUL 00 00 00000000 00000000 1000000 64 40 01000000 11000000 01000000 SOH 1 STX 02 00000010 10000010 000000010 B 66 42 01000010 01000010 11000010 ETX 0 00000011 EOT 04 00000100 10000100 00000100 D 68 44 01000100 01000100 f 11000100 5 00000101 00000101 400001001 JE 69 45 01000101 11000101 01000101 00000110 10000110 00000111 00000111 00001000 00001000 00001001 10001001 00001010 10001010 00001011 00001011 00001100 10001100 00001101 00001101 D 00001110 00001110 01001110 00001111 10001111 01001111 00010000 00010000 01010000 07070000 1101
13. number of registers to write low byte must be 0x01 CRC low byte CRC high byte Loop Back Command 0x08 This command simply echoes the message This serves as a quick way to check your wiring Packet sent to controller nn 08 nnnn nnnn A A A A controller address one byte loop back command 0x08 data high byte data low byte CRC low byte CRC high byte Example Run loop back test on controller at address 40 0x28 Sent 28 08 55 66 77 88 31 B7 Received 28 08 55 66 77 88 31 B7 Exception Responses When a controller cannot process a command it returns an exception response and sets the high bit 0x80 of the command 0x01 illegal command 0x02 illegal data address 0x03 illegal data value Packet returned by controller A controller address one byte command 0x80 exception code 0x01 or 0x02 or 0x03 CRC low byte CRC high byte Watlow Controls Communications Guide 16 Messages with the wrong format timing or CRC are ignored A read command sent to an inactive parameter returns 0x0000 Example Exception 01 Command 02 is not supported Sent 01 02 0001 00 02 A8 OB Received 01 82 01 81 60 Example Exception 02 The parameter at register 45 0x002D is inactive Sent 01 06 00 2D 00 01 D8 C3 Received 01 86 02 C3 A1 Example Exception 03 Cannot write 12 000 Ox2EEO to register 7 out of range illegal data value Sent 01
14. oarenien aaa ai a a een 10 Chapter 4 Write Your Own HMI 12 Purchase an HMI package 18 Chapter 5 Interface Adapters 20 Watlow Software Tools 20 922 Comm Diagnostic 21 Comma Diagnostic Software 21 Commb5vb Diagnostic Software 21 CRG as eee eee Bub t A Baie ss 21 Interface Comparison 22 Controller Comparison Summery 22 Appendix Glossary onna daa a a 23 Disclaimer of Warranty 28 A downloadable electronic copy of this user manual is available free of charge through Watlow s web site http www watlow com prodtechinfo Watlow Controls Communication Guide Chapter One Introduction Audience The document is targeted towards new users interested in using data communications with Watlow controllers Media This document is available in electronic format only It is viewable using Adobe Acrobat Reader available free from the Adobe site www adobe com on the World Wide Web Purpose The purpose of this document is to enable users to 1 Understand the basics of serial data communications via standard definitions interfaces and protocols 2 Setup and use a simple network of one Watlow controller 3 Setup and use a network of two or more Watlow controllers with HMI human machine interface software or an operator interface panel Getting Started Your tas
15. required to have a multi drop system more than one controller on the bus See the list below for some vendors who sell these converters Should your PC or PLC have the appropriate interface just connect using the wiring diagram supplied with your controller For EIA 422 the T connects to the R sometimes labeled B while the T connects to the R sometimes labeled A For EIA 485 the terminal marked A usually connects to the T R while the B terminal connects to the T R of the controller The standards do not specify the wire size and type Use of AWG 24 twisted pair provides excellent results If shielded cable is used terminate the shield at one end only Always follow the manufacturer s instructions supplied with the interface converter See Biasing of Buses next Biasing of Buses The EIA 485 standard requires the bus to be biased for reliable communication This means to provide termination resistors across the T R and T R wires One resistor is placed at the PC or PLC where it connects to the EIA 485 bus The second resistor is placed at the last controller on the network Do not place resistors at each controller The impedance of the wires used for the bus determines the resistor value For twisted pair the value is typically 120 ohms In addition it may be necessary to have a pull up and pull down resistor between the power supply and ground of the interface adapter Check the documentation
16. that came with your interface adapter Biasing the bus reduces reflection of signals sent down the bus These reflections are sometimes referred to as a standing wave This condition is most notable when communicating at high baud rates Interface Converters The purpose of an interface converter is to allow two different buses to be connected Interface converters are required when connecting an EIA 232 port to an EIA 422 or EIA 485 bus The EIA 422 bus is a full duplex bus This means that it can send and receive data at the same time The EIA 485 bus is a half duplex bus This means that it can only send or receive data at any given time Some interface converters on the market have provided the ability to have full duplex with the ELA 485 bus This is accomplished by using two receivers and transmitters tied in tandem This type of converter will not work with the Watlow controllers Be sure that the model you purchase is designed for half duplex Another consideration when using interface converters is how the converter handles switching between transmit and receive When connecting between an EIA 232 and an EIA 485 the converter must convert two items First it must convert the voltage level Second it must convert from half duplex to full duplex This 1s not an easy task Typically it is accomplished via a handshake line from Watlow Controls Communications Guide 10 the PC or PLC When data flows into the converter
17. 0 11110010 00110011 10110011 OT110011 1110011 91110011 00110100 00710700 01710700 1110100 11110100 00110101 10110101 01110101 1110101 01110101 00110110 10110110 OT110110 1110110 91110110 00110111 00710711 oriioiii mom mom 00111000 00111000 01111000 1111000 11111000 00111001 10111001 01117001 1111001 91111001 00111010 10111010 01717010 1111010 01711010 00111011 00111011 01111011 91111071 11111011 00111100 10111100 124 01117100 11111100 01711100 6t 3b jJoorior 40111101 fooi pD 25D OrtiTOT 01111107 11111101 gt 62 3E 00111110 40111110 00111110 126 zE 0tttftiO 01111110 11111110 The first digit in bold is the parity bit when enabled oo ACK Cl J 2 co Co cof co KIE KIS IE cof e co cof e S Do E no S no E PJ P Poo Po D De Ees S Ea PES 1S fa fam fe fem fem e OQ OO FS Cf cof NY DI BY cpr A SF aa SO A ca BJS cof NJ ca BJ co N 2 S Oo a co ES Of cof NI a oo BS cof ro OJ HI m m gt e SINT NT SI M MIT M MI NT NI OO Oo DI o 92 D gt gt gt OY Ooo oon oy LSN Sa of Caf of Cano BIB ESEN o of NID A co ro les CO Cot NI Op Copp T ie ap mo 5 gt gt O co e Le Ke f 0 cof oof oo SINT NT NINN Sisis NI SN SfN a CARS SO Ooo NI fon sy cl oo Aa 2 2 oe oliolice NI po sy a 2 2 NINININ C5 ro o pmi
18. 0000 00010001 10010001 01010001 1010001 01010001 00010010 10010010 01010010 1010010 01010010 00010011 00010011 01010011 1010011 11010011 00010100 10010100 01010100 1010100 01010100 00010101 00010101 01010101 1010101 11010101 00010110 00010110 01010110 1010110 11010110 00010111 10010111 01010111 1010111 01010111 00011000 10011000 01011000 1011000 01011000 00011001 90011001 01011001 1011001 11011001 00011010 00011010 01011010 1011010 11011010 00011011 10011011 01011011 1011011 91011011 00011100 00017700 01011100 1011100 01011100 00011101 10011101 01011101 1011101 01011101 00011110 10011110 a OT01T110 1011110 01011110 oooi ooi oon omm Tonm 00100000 00100000 01100000 1100000 11100000 00100001 10100001 01100001 1100001 01100001 00100010 10100010 01100010 1100010 01100010 00100011 00100011 01100011 1100011 11100011 00100100 10100100 01100100 1100100 01100100 00100101 00700701 01100101 1100101 11100101 00100110 00100110 01100110 1100110 11100110 00100111 10100111 OT100111 1100111 91100111 00101000 10101000 01101000 1101000 01101000 00101001 00101001 01101001 1101001 11101001 00101010 00101010 01101010 1101010 11101010 00101011 10101011 oTi0T011 Ti010T1 01707011 00101100 00101100 01101100 1101100 11101100 00101101 10101101 OT10T101 1101101 91101101 00101110 10101110 01107710 Ti01110 01707110 00101111 00101111 OTIOTTTI mot 11101111 00110000 10110000 01110000 1110000 01110000 00110001 00110001 01710001 1110001 11110001 00110010 00110010 01110010 111001
19. 2 interface uses five wires a talk pair a listen pair and a common line It can handle one master and up to ten remote devices in a multidrop more than one controller shares the same wires network up to 4 000 feet long EIA 422 uses the difference in voltage between the two wires to indicate a 1 ora 0 bit A 1 is a difference of 5 volts while a 0 is a difference of 5 volts EIA 423 Full Duplex An EIA 423 interface is compatible with EIA 232 It is a newer standard designed for more speed and distance It uses three wires a single transmit wire a single receive wire and a common line Only two devices can use an EIA 423 interface A 3 to 6 volt signal indicates a 1 and a 3 to 6 volt signal indicates a 0 The EIA 423 signal is referenced to the Watlow Controls Communications Guide common line rather than to a separate wire as in EIA 485 and EIA 422 An EIA 423 cable is limited up to 4 000 feet due to noise susceptibility EIA 485 Half Duplex An EIA 485 interface uses three wires a T R a T R and a common line A 5 volt signal is interpreted as a 1 a 5 volt signal as a 0 As many as 32 remote devices can be connected to a master on a multi drop network up to 4 000 feet long Wiring Most PCs and some PLCs have a standard EIA 232 port usually referred to as RS 232 In these instances you must use an interface converter to connect to EIA 422 or EIA 485 These interface standards are
20. CAUTION This manual is provided for reference only It does NOT provide instructions on how to operate your chamber The Series F4 Temperature Controller uses the Modbus protocol for communications Only the applicable sections related to Modbus in this manual apply Data Communications Reference Electronic User s Manual CUSTOMER SATISFACTION Er ISO 9001 LL AR NS Ma a SS WOW 7 SQ SLE Registered Company Winona Minnesota USA Bas LOW Watlow Controls 1241 Bundy Blvd P O Box 5580 Winona Minnesota USA 55987 5580 Phone 507 454 5300 Fax 507 452 4507 WTCDCE A pdf Made in the U S A June 1998 15 00 Safety Information We use note caution and warning symbols throughout this book to draw your attention to important operational and safety information A NOTE marks a short message to alert you to an important detail A CAUTION safety alert appears with information that is important for protecting your equipment and performance Be especially careful to read and follow all cautions that apply to your application A WARNING safety alert appears with Technical Assistance If you encounter a problem with your Watlow controller review all of your configuration information to verify that your selections are consistent with your application inputs outputs alarms limits etc If the problem persists after checking the above you can get technical assistance from your local
21. FF Application The great thing about XON XOFF protocol is the simplicity of communications The basic structure is to send information to the controller as needed until you receive an XOFF 0x13 You must wait until you receive an XON 0x11 before continuing The controller follows this same scheme There are no confirmations of commands sent This protocol is highly efficient in that few characters are sent to handle the flow of Watlow Controls Communications Guide 12 information This protocol is sometimes referred to as flow control The disadvantage of this protocol is lower reliability in ensuring that both parties receive the proper information In addition only two devices can be on a bus because no means is provided to address any controller Handling Error Codes ER2 All communications related error codes are ER2 error codes which means that they re not considered cause for a shutdown of the unit itself With XON XOFF flow control error codes may be generated but there will be no standard indication of this fact Therefore you may want to query the status of ER2 after each command sent to see if it was successful User Responsibility Users must refrain from altering prompts that do not appear on the controller s front panel or are not included on the specific model For example do not send an A2LO command to a unit not equipped with an alarm for output 2 Most Watlow controllers contain a registe
22. Record User s Manual Diagnostic Menu readings if applicable 1962 and has earned the reputation as an excellent supplier to original equipment manufacturers These OEMs and end users depend upon Watlow Controls to provide compatibly engineered controls that they can incorporate into their products with confidence Watlow Controls resides in a 100 000 square foot marketing engineering and manufac turing facility in Winona Minnesota 5580 phone 507 454 5300 fax 507 452 4507 The Watlow Controls Data Communications Guide is copyrighted by Watlow Winona Inc J une 1998 with all rights reserved 1454 Table of Contents Chapter 1 Audience 0002 ee 4 NICQIE TC 4 PUNDOSE cities aoe died eee ee 4 Getting Started 0020005 4 Convention oaa a ai aaia ga aia a aa a eee 4 Chapter 2 Elements of Machine to Machine Comm 5 Character Format 05 5 Bits and Bytes 020000055 5 ASCI 203 255 ga add dpt E ie 2 5 ASCII Chart 02 0 0 000000 6 Serial Communication 7 Parity BIIS css seek eg s pebiui ia eee 7 Start and Stop Bits 8 Baud Rate uaaa 8 Computer Languages 8 Syntax sedie DATUR E RAUS e Rs 8 Chapter 3 Interface Standards 9 Wing ga cceeds debe RR rem 9x onn 9 Biasing of Buses 2 220005 9 Interface Converters llssuun 10 Protocols
23. Watlow representative or by dialing 507 454 5300 ext 1111 An applications engineer will discuss your application with you About Watlow Controls Watlow Controls is a division of Watlow Electric Mfg Co St Louis Missouri a manufacturer of industrial electric heating products since 1922 Watlow begins with a full set of specifications and completes an industrial product that is manufac tured in house in the U S A Watlow products indude electric heaters sensors controllers and switching devices The Winona operation has been designing solid state electronic control devices since Your Feedback Y our comments or suggestions on this manual are welcome Please send them to the Technical Literature Team Watlow Controls 1241 Bundy Blvd P O Box 5580 Winona Minnesota 55987 information that is important for protecting you others and equipment from damage Pay very close attention to all warnings that apply to your application The safety alert symbol A an exdamation point in a triangle precedes a general CAUTION or WARNING statement The electrical hazard symbol N a lightning bolt in a triangle precedes an electric shock hazard CAUTION or WARNING safety statement Please have the following information available when calling Complete model number from the label on the side of the controller All configuration information User Profile Record Custom Main Page Record and Operations Page Parameter
24. ace Adapters 20 Interface Comparison 22 Interface Converters 10 Interface Standards 9 M Media 4 P Parity Bits 7 Protocols 10 Purchase an HMI package 18 Purpose 4 S Serial Communication 7 Start and Stop Bits 8 Syntax 8 W Watlow Software Tools 20 Wiring 9 Write Your Own HMI 12 Watlow Controls Communications Guide 29 How to Reach Us TOTAL USTOMER TISFACTION ry Quality and Mission Statement Watlow Controls will be the world s best supplier of industrial temperature control products services and systems by exceeding our customers employees and shareholders expectations Contact Your Authorized Watlow Distributor Phone 507 454 5300 Fax 507 452 4507 For technical support ask for an Applications Engineer To place an order ask for Customer Service To discuss a custom option ask for a Product Manager Warranty Most Watlow Controls are warranted to be free of defects in material and work manshi p for 36 months after delivery to the first purchaser for use providing that the units have not been misapplied Since Watlow has no control over their use and sometimes misuse we cannot guarantee against failure Watlow s obligations hereunder at Watlow s option are limited to replacement repair or refund of purchase price and parts which upon examination prove to be defec tive within the warranty period specified This warranty does not apply to
25. ase we have selected odd parity The number of 1s in the first seven bits plus the parity bit must always total an odd number The total number of 1s in the binary character 1010111 W is 5 already an odd number Thus our parity bit will be a 0 Watlow Controls Communications Guide If we were transmitting the lower case w binary 1110111 the parity bit would be a because the total number of 1 s in the character frame is 6 an even number Adding the parity bit makes it odd and consistent with the odd parity rule If a noise spike came onto the data line and changed the signal voltage level enough to reverse a to a 0 in the character frame the receiver would detect that error The total number of 1s would be even and a violation of the odd parity rule At Watlow we use odd even and no parity Odd parity sets the parity bit to 0 if there are an odd number of 1s in the first seven bitsEven parity sets the parity bit to 0 if there are an even number of 1s in the first seven bits No parity ignores the parity bit Start and Stop Bits A start bit informs the receiving device that a character is coming and a stop bit tells it that a character 1s complete The start bitis always a 0 The stop bit is always a 1 The human speech equivalent of these bits could be a clearing of the throat to get someone s attention start bit and a pause at the end of a phrase stop bit Both help the listener understand t
26. ble format RAM Floppy Disk Hard Disk Space Represents the transmission of a data bit logic 0 see logic level Usually this is the most positive voltage value in serial communications Start Bit A binary bit or logic level that represents when the serial data information is about to start at the beginning of a character or byte This voltage level is positive Stop Bit A binary bit or logic level that represents when the serial data information is complete at the end of a character or byte This voltage level is negative Synchronous When data is transmitted on a data line and a clock signal 1s used on another line to determine when to check the data line for a logic level This clock is said to synchronize the data TCP IP Transmission Control Protocol Internet Protocol is a software protocol used to send and receive data between different computer systems Standard protocol used on the Internet Transmit To send data from one device to another The device that sends the data is the transmitter Word Two bytes make a word This contains 16 bits XON XOFF A software protocol that controls the flow of serial information Sending an XON tells the transmitter to start sending information An XOFF tells the transmitter to stop sending until the receiver has processed the current information XOFF DC3 Control S hex 11 XON DC1 Control Q hex 13 Disclaimer of Warranty This is a gene
27. ed There is a limit to the number of times you can store information in the EPPROM PCs can quickly reach this limit if the set point is continually changed as in a ramping controller Disabling this feature will prevent this damage Care must also be taken that the process can not cause damage to property or injury to personnel if the wrong commands are sent due to operator error or equipment malfunction Be sure to use limit devices on the equipment to prevent system runaway Because of the wide array of choices available for setting up a Watlow controller only a subset of the prompts contains parameters in a given situation The user s manual explains the interrelations between prompts Writing a Modbus Application Modbus RTU enables a computer or PLC to read and write directly to registers containing the controller s parameters With it you could read all 141 of the controller s parameters with five read commands Because of the wide array of choices available for setting up a controller Watlow Controls Communications Guide 13 utilizing Modbus only a subset of the prompts contain parameters in a given situation This document explains the interrelations between prompts If you already have a software application that uses Modbus you can simply skip to the Temperature process Controller Prompt Table or the Modbus RTU Address Table in the user s manual for the address information your program will need The rest o
28. f this section on the Modbus provides information for writing a software application that uses Modbus 1 You need to code messages in eight bit bytes with no parity bit one stop bit 8 n 1 2 Negative parameter values must be written in twos complement format Parameters are stored in two byte registers accessed with read and write commandis to a relative address 3 Messages are sent in packets that are delimited by a pause at least as long as the time it takes to send 30 bits To determine this time in seconds divide 30 by your baud rate 4 Because changing some parameters automatically changes or defaults other parameters use the Complete Parameter Download Sequence table listed in the user s manual to order write commands Using a controller address of 0x00 for a write command will send that command to all the controllers in the network This is a powerful feature if all the controllers on a network use all or most of the same parameters Packet Syntax Each message packet begins with a one byte controller address from 0x01 to OxF7 The second byte in the message packet identifies the message command read 0x03 or 0x04 write 0x06 or 0x10 or loop back 0x08 The next n bytes of the message packet contain register addresses and or data The last two bytes in the message packet contain a two byte Cyclical Redundancy Checksum CRC for error detection Packet format nn nn nnn nnmn address CS F f co
29. from the PC a handshake line is placed high When data flows out of the converter to the PC the handshake line is placed low In this way the handshake line controls the direction of information Another method of achieving this 1s to use a built in timer The converter switches to transmit when a character is sent to it from the PC After a period of time when the PC has not transmitted the converter switches to a receive mode It is important that you understand how your converter accomplishes this task You are required to wire this feature or make settings on the converter to enable this function The PC will not talk to the controllers correctly with out properly setting this Your converter may also require settings through dip switches to set up communications parameters like baud rate data bits start bits stop bits and handshaking See the documentation that comes with your converter for more detail The converter may require a separate power supply Some converters get their power from the handshake lines of the PC If you rely on this method you will need to wire these additional lines In addition your software must set these lines high A more reliable method is to use the external power supply This 1s especially necessary when using a laptop computer Protocols Protocol describes how to initiate an exchange It also prevents two machines from attempting to send data at the same time There are a number of
30. he message Baud Rate The baud rate refers to the data transmission When a change in signal represents one data bit baud rate is equal to bits per second bps Standard baud rates for computers are 300 600 1200 2400 4800 9600 and 19200 baud Computer Languages Computer languages are simply sets of symbols and rules for their use There are many computer languages and a wide variety of applications for them Programmers use languages to enable computers to do real work Syntax Syntax for a natural language dictates how we put words together to make phrases and sentences In data communications syntax also dictates how we order the parts of a message Watlow Controls Communications Guide Chapter Three Watlow Controls Approach to Data Communications Interface Standards An interface is a means for electronic systems to interact It s a specific kind of electrical wiring configuration Four interfaces are commonly used EIA 232 Full Duplex An EIA 232 formerly RS 232 interface uses three wires a single transmit wire a single receive wire and a common line Only two devices can use an EIA 232 interface A 3 to 24 volt signal indicates a l and a 3 to 24 volt signal indicates a 0 The EIA 232 signal is referenced to the common line rather than to a separate wire as in EIA 485 and EIA 422 An EIA 232 cable is limited to 50 feet due to noise susceptibility EIA 422 Full Duplex The EIA 42
31. ically noisy environments Lastly purchase an interface controllers PC or PLC and software that will work together Software may be written to accomplish the task 1f you have the skills and resources to do so Watlow Controls Communications Guide 22 Appendix Glossary Address A unique designator for a location of data or a controller that allows each location or controller on a single communications bus to respond to its own message Similar to your own residence address ANSI American National Standards Institute ANSI x3 28 The American National Standards Institute developed this communication standard protocol This method uses a unique address for each device Only the master can initiate a communications session by sending an address and then the lt ENQ gt character All other messages must start with a start of text lt STX gt and end with an end of text lt ETX gt character The bus is released to the other device by sending lt EOT gt character Messages are lt ACK gt acknowledged or lt NAK gt negative acknowledged ASCII pronounced AS KEY American Standard Code for Information Interchange A universal standard for encoding alphanumeric characters into 7 or 8 binary bits Asynchronous Communications where characters can be transmitted at an unsynchronized point in time In other words it can start and stop anytime The time between transmitted characters may be of varying lengths Communicatio
32. k is to get one or more controllers to talk to a PC or PLC How do you make this happen The purpose of this document is to assist you in that task by providing information about communications The task of getting a PC or PLC communicating with controllers is a five step process 1 Determine a strategy for communications 2 Purchase a controller with a communication interface and protocol that supports your strategy 3 Wire controllers for power control and communication 4 Configure the controllers to do what you want them to do Watlow Controls Communications Guide 5 Configure the PC or PLC software and hardware to do what you want them to do The first step is the most difficult since decisions need to be made before anything is purchased It really involves three basic items 1 Determine how many controllers you will communicate with 2 Pick a protocol and interface that supports the information exchange 3 Purchase hardware and software to make this happen This document will only deal with the task of communication Refer to the user s manuals for each product for information about wiring and configuring the controllers and software Convention In this document numbers in the format 0x00 represent values in hexadecimal Numbers in the format 0 represent values in decimal and finally numbers in the format 00000000 represent values in binary unless stated otherwise Chapter 2 Definition of Term
33. ly or not at all Watlow has not tested the converters listed and this list is provided as informational only Watlow makes no claims as to the performance or compatibility with any converter B amp B Electronics 707 Dayton Road PO Box 1040 Ottawa IL 61350 Phone 815 433 5100 http www bb elec com Part 485OIC for EIA 232 to EIA 422 or EIA 485 Dataforth Corporation formerly supplied by Burr Brown 3331 E Hemisphere Loop Tucson AZ 85706 Phone 800 444 7644 Part LDM422 for EIA 232 to EIA 422 Part LDM485 for EIA 232 to EIA 485 CMC Connecticut Microcomputer Corporation Watlow Software Tools 920Comm Diagnostic Software Watlow has a program available free of charge called 920COMM EXE that is used with the Series 920 Controller This can be downloaded from our BBS at 507 452 3958 This is a terminal program that handles the protocol for you The program can be used to determine if your cables are properly connected and that the controller is working This program supports the ANSI x3 28 and XON XOFF protocols 922 Comm Diagnostic Software Another program available free of charge is called 922COMM EXE which is used with the Series 922 Controller This can be downloaded from our BBS at 507 452 3958 This is a terminal program that handles the protocol for you The program can be used to determine if your cables are properly connected and that the controller is working This program supports the
34. mmand registers and or data CRC Read Multiple Registers Command 0x03 or 0x04 This command returns from 1 to 32 registers Packet sent to controller nn 03 nnnn 00nn nnnn A A A A A A A A controller address one byte read command 0x03 or 0x04 starting register high byte starting register low byte number of registers high byte 0x00 number of registers low byte CRC low byte CRC high byte Packet returned by controller nn 03 nn nnnn nnnn nnnn 4 i A A A A A controller address one byte read command 0x03 or 0x04 number of bytes one byte first register data low byte first register data high byte register n data high byte register n data low byte CRC low byte CRC high byte Watlow Controls Communications Guide 14 Example 988 only Read register 0 model number of the controller at address 1 Sent 01 03 00 00 00 01 84 OA Received 01 03 02 03 DC B9 2D Message 988 0x03DC Example 988 only Read register 1 and 2 Process 1 and 2 values of controller at address 5 Sent 05 03 00 01 00 02 94 4F Received 05 03 04 00 64 00 C8 FF BA Message 100 0x0064 and 200 0x00C8 Write to a Single Register Command 0x06 This command writes a parameter to a single register The controller will echo back the command An attempt to write to a read only parameter returns an illegal data address
35. n is controlled by start and stop bits at the beginning and end of each character Baud Unit of signaling speed derived from the number of events per second normally bits per second Baud rate The rate of information transfer in serial communications measured in bits per second Watlow Controls Communications Guide 23 Binary Number based system where only two characters exist 0 and 1 Counting is 0 1 10 11 Bit Derived from BInary DigiT a one or zero condition in the binary system Byte A term referring to eight associated bits of information sometimes called a character CAN Bus The Controller Area Network Bus is a serial communications protocol that includes software and hardware CAN was originally developed by the German company Robert Bosch for use in the auto industry to provide a cost effective communications bus for in car electronics Character Letter numeral punctuation control figure or any other symbol contained in a message Typically this is encoded in one byte Communications The use of digital computer messages to link components See serial communications and baud rate Converter This device will convert from one hardware interface to another such as from EIA 232 to EIA 485 The converter may be transparent to the software which means you do not have to give any special considerations to software programming CRC When data is corrupted during tra
36. nsmission a method is used to return the data to its correct value This can be accomplished through several methods parity checksum and CRC cyclic redundancy checksum are three of these Cyclic Redundancy Checksum is an error checking mechanism using a polynomial algorithm based on the content of a message frame at the transmitter and included in a field appended to the frame At the receiver it is then compared with the results of the calculation that is performed by the receiver Data The information that is transferred across the communications bus This may be a setpoint setup parameter or any character This information is transferred to an address or register DB 9 A standardized connector shaped like the letter D when viewed on edge This connector has 9 contacts It is utilized on most IBM AT compatible PCs as the serial port DB 15 A standardized connector shaped like the letter D when viewed on edge This connector has 15 contacts It is utilized on most IBM AT compatible PCs as the game midi port DB 25 A standardized connector shaped like the letter D when viewed on edge This connector has 25 contacts It is utilized on most IBM AT compatible PC s as the parallel port when the PC end contains socket contacts Can also be the serial port when the PC end contains pin contact Decode This is the reverse of encode When a piece of data has information embedded in it decode is to extract that info
37. performance or compatibility with any HMI software package Anawin by Watlow Anafaze 334 Westridge Drive Watsonville CA 95076 Phone 408 724 3800 http www watlow com WATLINK by Watlow Controls 1241 Bundy Blvd Winona MN 55987 Phone 507 454 5300 http www watlow com CONTROLWARE by Controlware 245 Northland Blvd Cincinnati OH 45246 3603 Phone 800 776 9704 http www controlware com Cimplicity by GE Fanuc Phone 1 800 648 2001 http www gefanuc com Genesis by Iconics 100 Foxborough Blvd Foxborough MA 02035 Phone 800 946 9679 http www iconics com Interact by CTC 50 W TechneCenter Drive Milford OH 45150 Phone 513 831 2340 http www ctcusa com KEPware MMI by KEPware Inc 81 Bridge Street Yarmouth ME 04096 Phone 207 846 5881 http www kepware com LabView by National Instruments 6504 Bridge Point Parkway Austin TX 78730 5039 Phone 512 794 0100 http www natinst com Lookout by National Instruments 6504 Bridge Point Parkway Austin TX 78730 5039 Phone 512 794 0100 http www natinst com Modbus for Windows by Calta Computer Systems Ltd 230 550 71 Ave SE Calgary Alberta Canada T2H 0S6 Phone 403 252 5094 http www calta com OI 2000 by Software Horizons Inc 10 Tower Office Park Suite 200 Woburn MA 01801 2120 Phone 617 933 3747 http www shorizons com Spec View by SpecView LLC 41 Canyon Green Court San Ramon CA 94583 Phone 510 275 0600 h
38. r are not included on the specific model For example do not send an A2LO command to a unit not equipped with an alarm for output 2 Most of Watlow controllers contain a register to disable saving of the current set point to EEPROM When using your PC or PLC to control the set point in the Watlow controller the EEPROM may be prematurely damaged There is a limit to the number of times you can store information in the EPPROM PCs can quickly reach this limit if the set point is continually changed as in a ramping controller Disabling this feature will prevent this damage Care must also be taken that the process can not cause damage to property or injury to personnel if the wrong commands are sent due to operator error or equipment malfunction Be sure to use limit devices on the equipment to prevent system runaway Purchase an HMI package Not all HMIs are equal in performance Set up and operation function of each Watlow Controls Communications Guide 18 manufacturer s HMI package is unique Industrial controllers operate in a harsh electrically noisy environment This can cause less robust HMIs to work intermittently or not at all In addition the platform PC or PLC which runs the HMI is subject to failures causing unpredictable operation of your process Watlow has not tested the HMIs listed with the exception of ANAWIN and WATLINK This list is provided as informational only Watlow makes no claims as to the
39. r to disable saving of the current set point to EEPROM When using your PC or PLC to control the set point in the Watlow controller the EEPROM may be prematurely damaged There is a limit to the number of times you can store information in the EPPROM PCs can quickly reach this limit if the set point is continually changed as in a ramping controller Disabling this feature will prevent this damage Care must also be taken that the process can not cause damage to property or injury to personnel if the wrong commands are sent due to operator error or equipment malfunction Be sure to use limit devices on the equipment to prevent system runaway Writing an ANSI x3 28 Application Handling Error Codes ER2 All communications related error codes are ER2 error codes which means that they re not considered cause for a shutdown of the unit itself There is always a communications error code generated when the lt NAK gt character 0x15 is sent under the ANSI x3 28 protocol User Responsibility Users must refrain from altering prompts that do not appear on the controller s front panel or are not included on the specific model For example do not send an A2LO command to a unit not equipped with an alarm for output 2 Most of Watlow controllers contain a register to disable saving of the current set point to EEPROM When using your PC or PLC to control the set point in the Watlow controller the EEPROM may be prematurely damag
40. ral overview and statement of the safety related need for and methods of applying data comunications for temperature processes Because of the diversity of conditions and hazards under which control products may be applied and because of the differences in components and methods of their installation no representation or warranty of any kind express or implied is hereby made that the data comunications discussed and presented herein will be effective in any particular application or set of circumstances or that addi tional or different precautions will not be reasonably necessary for a parti cular application We will be pleased to consult with you regarding a specific application upon request Trademark Information Watlow Gordon Anafaze ANASOFT ANAWIN MICRODIN are trademarks of Watlow Electric Manufacturing Company Modbus is a trademark of AEG Schneider Automation Windows and Microsoft are trademarks of the Microsoft Corporation Watlow Controls Communications Guide 28 Index A 922 Comm Diagnostic 21 Appendix 23 ASCII Chart 6 ASCII 5 Audience 4 B Baud Rate 8 Biasing of Buses 9 Bits and Bytes 5 C Character Format 5 Comma Diagnostic Software 21 Commbvb Diagnostic Software 21 Computer Languages 8 Controller Comparison Summery 22 Convention 4 CRC 21 D Disclaimer of Warranty 28 Elements of Machine to Machine Comm 5 G Getting Started 4 Glossary 23 l Interf
41. re on a personal computer Also called HMI Network When two or more devices share communications lines the devices are networked Node A point of interconnection to a network Noise Immunity The ability of communications lines to ignore electrical noise generated in the communications lines by nearby magnetic and electrostatic fields Odd This term 1s used with parity See parity OSI Open Systems Interconnection are those which conform to specifications and guidelines that are open to all This allows equipment from any manufacturer which claims to comply with the standard to be used interchangeably on the standard network Watlow Controls Communications Guide 26 Parallel Communication using this method transfers eight bits or one byte at a time over eight data wires and one ground wire This method is eight times faster than using serial but utilizes more hardware Parity A bit is assigned at the beginning of a byte to stand for parity When the 1 bits are counted the number will be even or odd A parity bit is used to ensure that the answer is always even if even parity or odd if odd parity If the receiving end counts the 1 bits and the sum is not the same odd or even an error is generated Ex 00010000 has an odd number of 1s In even parity we would set the parity to 1 so we have an even number of bits In odd parity we would set the parity bit to 0 so we have an odd number of 1
42. rmation Ex To extract an A from 01000001 DeviceNet A software protocol hardware interface based on CAN A low cost communication link that connects industrial devices over a network Uses twisted pair wires for the power and bus Nodes can be removed or inserted on the bus without powering down the network Double Word Equivalent to two words or four bytes This equals 32 bits Duplex The ability to send and receive data at the same time To listen and talk at the same time Watlow Controls Communications Guide 24 EIA See Electronic Industries Association EIA 232 Electronic Industries Association developed this standard hardware interface to allow one device to talk to another device in full duplex mode This method uses a differential voltage between one wire and ground Also called an unbalanced system since the ground wire carries the sum of current of all lines First standard to gain wide acceptance by manufacturers Transmission is limited to about 50 feet EIA 422 Electronic Industries Association developed this standard hardware interface to allow up to 10 devices to be on a bus at one time This method uses a differential voltage between two wires Also called a balanced system since each wire carries the same current values This has the advantage of being immune to outside electrical disturbances EIA 423 Electronic Industries Association developed this standard hardware interface to allo
43. rmation in the controller These registers are listed in your user s manual You will need this list to determine where the data is located The last item sent in the packet is a field to ensure the data is received intact This is called a cyclic redundancy check sum All information exchanged is in hex numbers Watlow only supports the binary version of Modbus referenced as RTU The ASCII version is less efficient and is not supported Chapter Four Human Machine Interfaces HMI HMI stands for Human Machine Interface and is sometimes referred to as Man Machine Interface MMI This is an operator interface that allows you to monitor and control your process Many software packages were written to allow a PC to perform this function Use care in selecting software packages Some will run only under a specific disk operating system such as Windows NT from Microsoft The serial interface and protocol must match between the PC or PLC and the controller Many companies provide free working demonstration copies Obtain a demonstration copy so you can see if the program meets your needs Listed below are a few of the many software packages that claim to support the Modbus protocol Watlow does not recommend any one software package nor supports the implementation of any software package not sold by Watlow Contact the software manufacturer for more information in applying their software Write your own HMI Writing an XON XO
44. s Elements of Machine to Machine Communication In human communication there are basic words and sentences used to get a message across Likewise with computers and controllers They need a code called a character format or character set They need rules called protocol to govern their conversation and prevent confusion and errors Computers need a connecting interface over which to communicate They may use one pair of wires to send information in one direction and another pair to send in the opposite direction full duplex Or they may use one pair to send in both directions half duplex Character Format The code or character formats for Watlow data communication is shared by virtually everyone in the electronics business everywhere This code defines a computer stream of 1 s and 0 s that are created by varying a voltage signal in a regular manner The code is the American Standard Code for Information Interchange called ASCII asky Watlow Controls Communications Guide Bits and Bytes The word bit is simply the contraction of the words binary digit A bit is the basic unit in ASCII It is either a 1 or a 0 A byte is a string of seven or eight bits that a computer treats as a single character ASCII requires seven bits to represent each letter of the alphabet each digit and each punctuation mark we use ASCII The ASCII code defines 128 separate seven or eight bit characters see chart below one
45. ttp www specview com Watlow Controls Communications Guide Visual Logic Controller by Steeplechase Software Inc 1330 Eisenhower Place Ann Arbor MI 48108 Phone 313 975 8100 http www steeplechase com Wonderware 2000 by Wonderware Corp 100 Technology Drive Irvine CA 92718 Phone 714 727 3200 http www wonderware com Chapter Five Operator Interface Panels Not all Operator Interface Panels are equal in performance Programming of each manufacturer s panel is unique Industrial controllers operate in a harsh electrically noisy environment This can cause less robust panels to work intermittently or not at all Watlow has not tested the panels listed and this list is provided as informational only Watlow makes no claims as to the performance or compatibility with any Operator Interface Panel EXOR 4740T Interstate Drive Cincinnati OH 45246 Phone 513 874 4665 http www exor rd com CTC 50 W TechneCenter Drive Milford OH 45150 Phone 513 831 2340 http www ctcusa com Maple Systems 1930 220 Street SE Suite 101 Bothell WA 98021 Phone 425 486 4477 http www maple systems com Advantech Phone 1 800 800 6889 http www advantech usa com Interface Adapters Not all converters are equal in performance Industrial controllers Watlow Controls Communications Guide 20 operate in a harsh electrically noisy environment This can cause less robust converters to work intermittent
46. w one device to talk to another device in full duplex mode This method uses a differential voltage between one wire and ground Also called an unbalanced system since the ground wire carries the sum of current of all lines This standard is compatible with EIA 232 The outputs were beefed up to allow transmission up to 4000 ft EIA 485 Electronic Industries Association developed this standard hardware interface to allow up to 32 devices to be on a bus at one time This method uses a differential voltage between two wires Also called a balanced system since each wire carries the same current value This has the advantage of being immune to outside electrical disturbances EIA TIA 232 422 423 and 485 Data communications standards set by the Electronic Industries Association and Telecommunications Industry Association Formerly referred to as RS Recommended Standard See EIA 232 EIA 422 EIA 423 and EIA 485 Electronic Industries Association EIA An association in the US that establishes standards for electronics and data communications Encode To embed information into a piece of data This is the reverse of decode Ex Let s let 01000001 stand for an A Error Correction When an inconsistency is in the data a method is used to detect and or return the data to its correct value This can be done through several methods parity checksum and CRC cyclic redundancy checksum are a three of these Ethernet
47. with the CRC crc unsigned int char ptr Loop through all 8 data bits bit count 0 doi If the LSB is 1 shift the CRC and XOR the polynomial mask with the CRC if crc amp 0x0001 1 cre gt gt 1 cre POLYNOMIAL j If the LSB is 0 shift the CRC only else cre gt gt 1 while bit_count lt 7 while char_ptr lt end of packet return crc Interface Comparison Interface Maximum Max ft Cable Voltage Balanced Duplex Standard Bus Length Controllers Type Level Unbalanced EIA 232 50feet 1 3 wire 3 24v Unbalanced Full EIA 423 4 000feet 1 3 wire 3 12v Unbalanced Full EIA 422 4 000feet 10 5 wire 2 0 6v Balanced Full EIA 485 4 000 feet 32 3 wire 1 6 6v Balanced Hal Summary As first stated in this article the steps involved to communicate are 1 Determine how many controllers you will communicate with 2 Pick a protocol and interface that supports the information exchange 3 Purchase hardware and software to make this happen The number of controlled zones will determine the number of controllers connected to the PC or PLC Pick a protocol that will support this number Consider speed and reliability of communications when picking the protocol Ask yourself how will the devices understand each other Pick an interface that will support the number of devices connected transmit over the desired distance and is industrially hardened will communicate in electr
48. wo devices establishing a connection Using extra wires or software signals to coordinate communications signals can be sent to tell the transmitter the current status of the other device receiver Ex Are you busy or are you ready Hex or Hexadecimal Number based system where sixteen characters exist 0 to 9 A to F Counting is 0 9 A B C HMI Human to Machine Interface typically performed in software on a personal computer Also called MMI TEEE488 Bus developed by Hewlett Packard in 1965 as HP IB Also referred to as GPIB General Purpose Interface Bus Consist of 8 data lines and 8 control lines Bus length limited to 20 0 meters Supports 15 devices on the bus at one time Logic Level A voltage measurement system where only two stable voltage values exist Ex Ov and 5V or 3v and 3v Mark Represents the transmission of data bit logic 1 see logic level Usually this is the most negative voltage value in serial communications Master The device on the bus that controls all communications Only the master can initiate conversation Modbus A software protocol developed by Gould Modicon now AEG for process control systems No hardware interface is defined Modbus is accessed on the master slave principle the protocol providing for one master and up to 247 slaves Only the master can initiate a transaction This is a half duplex protocol MMI Man to Machine Interface typically performed in softwa
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