CAUTION - TestEquity

! 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.

WTCDCE_A.pdf Made in the U.S.A.June 1998 $15.00

Electronic User’s Manual

Registered Company Winona, Minnesota USA

ISO 9001ISO 9001

Data Communications Reference

Watlow Controls1241 Bundy Blvd., P.O. Box 5580, Winona, Minnesota USA 55987-5580, Phone: (507) 454-5300, Fax: (507) 452-4507

Safety InformationWe use note, caution and warning symbolsthroughout this book to draw your attention toimportant operational and safety information.

A “ NOTE”marks a short message to alert you toan important detail.

A “CAUTION” safety alert appears withinformation that is important for protecting yourequipment and performance. Be especially carefulto read and follow all cautions that apply to yourapplication.

A “WARNING” safety alert appears with

information that is important for protecting you,others and equipment from damage. Pay very closeattention to all warnings that apply to yourapplication.

The safety alert symbol, , (an exclamation pointin a triangle) precedes a general CAUTION orWARNING statement.

The electrical hazard symbol, , (a lightning boltin a triangle) precedes an electric shock hazardCAUTION or WARNING safety statement.

Technical AssistanceIf you encounter a problem with your Watlowcontroller, 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 Watlow representative, or by dialing (507) 454-5300, ext. 1111. An applications engineer will discuss your application with you.

Please have the following informationavailable when calling:

• Complete model number (from the label on theside of the controller)

• All configuration information,User Profile Record, Custom Main Page Recordand Operations Page Parameter Record

• User’s Manual • Diagnostic Menu readings (if applicable)

Your FeedbackYour comments or suggestions on this manual arewelcome. Please send them to the TechnicalLiterature Team, Watlow Controls, 1241 BundyBlvd., P.O. Box 5580, Winona, Minnesota, 55987-

5580; phone: (507) 454-5300; fax: (507) 452-4507.The Watlow Controls Data Communications Guide is copyrighted by Watlow Winona, Inc., © June 1998, with all rights reserved. (1454)

Watlow Controls is a division of Watlow ElectricMfg. Co., St. Louis, Missouri, a manufacturer ofindustrial electric heating products since 1922.Watlow begins with a full set of specifications andcompletes an industrial product that is manufac-tured in-house, in the U.S.A. Watlow productsinclude electric heaters, sensors, controllers andswitching devices. The Winona operation has beendesigning solid-state electronic control devices since

1962, and has earned the reputation as an excellentsupplier to original equipment manufacturers.These OEMs and end users depend upon WatlowControls to provide compatibly engineered controlsthat they can incorporate into their products withconfidence. Watlow Controls resides in a 100,000-square-foot marketing, engineering and manufac-turing facility in Winona, Minnesota.

About Watlow Controls

Watlow Contro ls Communicat ion Guide 3

Chapter 1Audience . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Media . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4

Purpose . . . . . . . . . . . . . . . . . . . . . . . . . . . .4

Getting Started . . . . . . . . . . . . . . . . . . . . . . .4

Convention . . . . . . . . . . . . . . . . . . . . . . . . . .4

Chapter 2Elements of Machine to Machine Comm. . . .5

Character Format . . . . . . . . . . . . . . . . . . . . .5

Bits and Bytes . . . . . . . . . . . . . . . . . . . . . . .5

ASCII . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5

ASCII Chart . . . . . . . . . . . . . . . . . . . . . . . . .6

Serial Communication . . . . . . . . . . . . . . . . . .7

Parity Bits . . . . . . . . . . . . . . . . . . . . . . . . . . .7

Start and Stop Bits . . . . . . . . . . . . . . . . . . . .8

Baud Rate . . . . . . . . . . . . . . . . . . . . . . . . . .8

Computer Languages . . . . . . . . . . . . . . . . . .8

Syntax . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8

Chapter 3Interface Standards . . . . . . . . . . . . . . . . . . .9

Wiring . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9

Biasing of Buses . . . . . . . . . . . . . . . . . . . . . .9

Interface Converters . . . . . . . . . . . . . . . . . .10

Protocols . . . . . . . . . . . . . . . . . . . . . . . . . .10

Chapter 4Write Your Own (HMI) . . . . . . . . . . . . . . . . .12

Purchase an HMI package . . . . . . . . . . . . .18

Chapter 5Interface Adapters . . . . . . . . . . . . . . . . . . .20

Watlow Software Tools . . . . . . . . . . . . . . . .20

922 Comm Diagnostic . . . . . . . . . . . . . . . .21

Comm4 Diagnostic Software . . . . . . . . . . . .21

Comm5vb Diagnostic Software . . . . . . . . . .21

CRC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .21

Interface Comparison . . . . . . . . . . . . . . . . .22

Controller Comparison Summery . . . . . . . .22

AppendixGlossary . . . . . . . . . . . . . . . . . . . . . . . . . . .23

Disclaimer of Warranty . . . . . . . . . . . . . . . .28

Table of ContentsT

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 Communications Guide 4

Chapter One -Introduction

AudienceThe document is targeted towards newusers interested in using datacommunications with Watlow controllers.

MediaThis document is available in electronicformat only. It is viewable using AdobeAcrobat Reader available free from theAdobe site www.adobe.com on theWorld Wide Web.

PurposeThe purpose of this document is to enableusers to:1. Understand the basics of serial data

communications via standarddefinitions, interfaces and protocols.

2. Set up and use a simple network of oneWatlow controller.

3. Set up and use a network of two ormore Watlow controllers with HMI(human-machine interface) softwareor an operator interface panel.

Getting StartedYour task is to get one or more controllersto talk to a PC or PLC. How do you makethis happen? The purpose of thisdocument is to assist you in that task byproviding information aboutcommunications. The task of getting a PCor PLC communicating with controllers isa five step process:

1. Determine a strategy forcommunications.

2. Purchase a controller with acommunication interface andprotocol that supports yourstrategy.

3. Wire controllers for power, controland communication.

4. Configure the controllers to dowhat you want them to do.

5. Configure the PC or PLC softwareand hardware to do what you wantthem to do.

The first step is the most difficult sincedecisions need to be made before anythingis purchased. It really involves three basicitems:

1. Determine how many controllersyou will communicate with.

2. Pick a protocol and interface thatsupports the information exchange.

3. Purchase hardware and software tomake this happen.

This document will only deal with the taskof communication. Refer to the user’smanuals for each product for informationabout wiring and configuring thecontrollers and software.

ConventionIn this document, numbers in the format0x00 represent values in hexadecimal.Numbers in the format 0 represent valuesin decimal and finally, numbers in theformat 00000000 represent values inbinary unless stated otherwise.


Chapter 2 -Definition of Terms

Elements of Machine-to-Machine CommunicationIn human communication there are basicwords and sentences used to get a messageacross. Likewise, with computers andcontrollers. They need a code called acharacter format or character set. Theyneed rules called protocol to govern theirconversation and prevent confusion anderrors. Computers need a connectinginterface over which to communicate.They may use one pair of wires to sendinformation in one direction and anotherpair to send in the opposite direction (fullduplex). Or they may use one pair to sendin both directions (half duplex).

Character FormatThe code or character formats for Watlowdata communication is shared by virtuallyeveryone in the electronics businesseverywhere. This code defines a computerstream of 1’s and 0’s, that are created byvarying a voltage signal in a regularmanner. The code is the AmericanStandard Code for InformationInterchange, called ASCII (asky).

Bits and BytesThe word bit is simply the contraction ofthe words binary digit . A bit is the basicunit in ASCII. It is either a “1” or a “0”.A byte is a string of seven or eight bitsthat a computer treats as a singlecharacter. ASCII requires seven bits torepresent each letter of the alphabet, eachdigit and each punctuation mark we use.

ASCIIThe ASCII code defines 128 separateseven- or eight-bit characters (see chartbelow), one for each letter, digit andpunctuation mark. ASCII also includescontrol characters similar to those we findon computer keys, such as backspace, shiftand return. It also has ninecommunications control characters foridentification, enquiry (inquiry), start oftext, end of text, end of transmission,acknowledge, negative acknowledge andescape.

The ASCII code is sometimes written in abase-16 number system that is calledhexadecimal or “hex” for short. Thenumbers 0 through 9 represents the firstten digits of this system, and the letters Athrough F represents the final six digits.The 128 ASCII character code with thedecimal and hexadecimal equivalents islisted below.


ASCII ChartASCIIChar

Dec Hex No Parity7 or 8 bit

7 bit w/ EvenParity

7 bit w/ OddParity

ASCIIChar

Dec Hex No Parity7 or 8 bit

7 bit w / EvenParity

7 bit w/ OddParity

NUL 00 00 00000000 00000000 10000000 @ 64 40 01000000 11000000 01000000SOH 01 01 00000001 10000001 00000001 A 65 41 01000001 01000001 11000001STX 02 02 00000010 10000010 00000010 B 66 42 01000010 01000010 11000010ETX 03 03 00000011 00000011 10000011 C 67 43 01000011 11000011 01000011EOT 04 04 00000100 10000100 00000100 D 68 44 01000100 01000100 11000100ENQ 05 05 00000101 00000101 10000101 E 69 45 01000101 11000101 01000101ACK 06 06 00000110 00000110 10000110 F 70 46 01000110 11000110 01000110BEL 07 07 00000111 10000111 00000111 G 71 47 01000111 01000111 11000111BS 08 08 00001000 10001000 00001000 H 72 48 01001000 01001000 11001000HT 09 09 00001001 00001001 10001001 I 73 49 01001001 11001001 01001001LF 10 0A 00001010 00001010 10001010 J 74 4A 01001010 11001010 01001010VT 11 0B 00001011 10001011 00001011 K 75 4B 01001011 01001011 11001011FF 12 0C 00001100 00001100 10001100 L 76 4C 01001100 11001100 01001100CR 13 0D 00001101 10001101 00001101 M 77 4D 01001101 01001101 11001101SO 14 0E 00001110 10001110 00001110 N 78 4E 01001110 01001110 11001110SI 15 0F 00001111 00001111 10001111 O 79 4F 01001111 11001111 01001111DLE 16 10 00010000 10010000 00010000 P 80 50 01010000 01010000 11010000DC1 17 11 00010001 00010001 10010001 Q 81 51 01010001 11010001 01010001DC2 18 12 00010010 00010010 10010010 R 82 52 01010010 11010010 01010010DC3 19 13 00010011 10010011 00010011 S 83 53 01010011 01010011 11010011DC4 20 14 00010100 00010100 10010100 T 84 54 01010100 11010100 01010100NAK 21 15 00010101 10010101 00010101 U 85 55 01010101 01010101 11010101SYN 22 16 00010110 10010110 00010110 V 86 56 01010110 01010110 11010110ETB 23 17 00010111 00010111 10010111 W 87 57 01010111 11010111 01010111CAN 24 18 00011000 00011000 10011000 X 88 58 01011000 11011000 01011000EM 25 19 00011001 10011001 00011001 Y 89 59 01011001 01011001 11011001SUB 26 1A 00011010 10011010 00011010 Z 90 5A 01011010 01011010 11011010ESC 27 1B 00011011 00011011 10011011 [ 91 5B 01011011 11011011 01011011FS 28 1C 00011100 10011100 00011100 \ 92 5C 01011100 01011100 01011100GS 29 1D 00011101 00011101 10011101 ] 93 5D 01011101 11011101 01011101RS 30 1E 00011110 00011110 10011110 ^ 94 5E 01011110 11011110 01011110US 31 1F 00011111 10011111 00011111 _ 95 5F 01011111 01011111 11011111SP 32 20 00100000 10100000 00100000 ` 96 60 01100000 01100000 11100000! 33 21 00100001 00100001 10100001 a 97 61 01100001 11100001 01100001“ 34 22 00100010 00100010 10100010 b 98 62 01100010 11100010 01100010# 35 23 00100011 10100011 00100011 c 99 63 01100011 01100011 11100011$ 36 24 00100100 00100100 10100100 d 100 64 01100100 11100100 01100100% 37 25 00100101 10100101 00100101 e 101 65 01100101 01100101 11100101& 38 26 00100110 10100110 00100110 f 102 66 01100110 01100110 11100110‘ 39 27 00100111 00100111 10100111 g 103 67 01100111 11100111 01100111( 40 28 00101000 00101000 10101000 h 104 68 01101000 11101000 01101000) 41 29 00101001 10101001 00101001 i 105 69 01101001 01101001 11101001* 42 2A 00101010 10101010 00101010 j 106 6A 01101010 01101010 11101010+ 43 2B 00101011 00101011 10101011 k 107 6B 01101011 11101011 01101011, 44 2C 00101100 10101100 00101100 l 108 6C 01101100 01101100 11101100- 45 2D 00101101 00101101 10101101 m 109 6D 01101101 11101101 01101101. 46 2E 00101110 00101110 10101110 n 110 6E 01101110 11101110 01101110/ 47 2F 00101111 10101111 00101111 o 111 6F 01101111 01101111 111011110 48 30 00110000 00110000 10110000 p 112 70 01110000 11110000 011100001 49 31 00110001 10110001 00110001 q 113 71 01110001 01110001 111100012 50 32 00110010 10110010 00110010 r 114 72 01110010 01110010 111100103 51 33 00110011 00110011 10110011 s 115 73 01110011 11110011 011100114 52 34 00110100 10110100 00110100 t 116 74 01110100 01110100 111101005 53 35 00110101 00110101 10110101 u 117 75 01110101 11110101 011101016 54 36 00110110 00110110 10110110 v 118 76 01110110 11110110 011101107 55 37 00110111 10110111 00110111 w 119 77 01110111 01110111 111101118 56 38 00111000 10111000 00111000 x 120 78 01111000 01111000 111110009 57 39 00111001 00111001 10111001 y 121 79 01111001 11111001 01111001: 58 3A 00111010 00111010 10111010 z 122 7A 01111010 11111010 01111010; 59 3B 00111011 10111011 00111011 { 123 7B 01111011 01111011 11111011< 60 3C 00111100 00111100 10111100 | 124 7C 01111100 11111100 01111100= 61 3D 00111101 10111101 00111101 } 125 7D 01111101 01111101 11111101> 62 3E 00111110 10111110 00111110 ~ 126 7E 01111110 01111110 11111110? 63 3F 00111111 00111111 10111111 DEL 127 7F 01111111 11111111 01111111

The first digit in bold is the parity bit when enabled.


Serial Communication ASCII Control CodesThe interfaces we’ve chosen employ serialcommunication, which is the exchange ofdata in a one-bit-at-a-time, sequentialmanner on a single data line or channel.

Serial contrasts with parallelcommunication, which sends several bitsof information simultaneously over multiple lines or channels. Not only is serial data communication simpler than parallel, it is also less costly

ASCII Control Codes are used to giveinstructions to the remote device andresult in specific actions, such as a linefeed instruction on a printer.

ASCIIChar

Dec Hex Ctrl KeyEquiv.

Definition ASCIIChar

Dec Hex Ctrl KeyEquiv.

Definition

NUL 00 00 Crtl @ Null Character DC1 17 11 Crtl Q Data Control 1 - XONSOH 01 01 Crtl A Start of Header DC2 18 12 Crtl R Data Control 2STX 02 02 Crtl B Start of Text DC3 19 13 Crtl S Data Control 3 - XOFFETX 03 03 Crtl C End of Text DC4 20 14 Crtl T Data Control 4EOT 04 04 Crtl D End of Transmission NAK 21 15 Crtl U Negative AcknowledgeENQ 05 05 Crtl E Enquiry SYN 22 16 Crtl V Synchronous IdleACK 06 06 Crtl F Acknowledge ETB 23 17 Crtl W End of Trans BlockBEL 07 07 Crtl G Bell CAN 24 18 Crtl X CancelBS 08 08 Crtl H Back Space EM 25 19 Crtl Y End of MediumHT 09 09 Crtl I Horizontal Tabulation SUB 26 1A Crtl Z SubstituteLF 10 0A Crtl J Line Feed ESC 27 1B Crtl [ EscapeVT 11 0B Crtl K Vertical Tabulation FS 28 1C Crtl \ File SeparatorFF 12 0C Crtl L Form Feed GS 29 1D Crtl ] Group SeparatorCR 13 0D Crtl M Carriage Return RS 30 1E Crtl | Record SeparatorSO 14 0E Crtl N Shift Out US 31 1F Crtl _ Unit SeparatorSI 15 0F Crtl O Shift In SP 32 20 SpaceDLE 16 10 Crtl P Data Link Escape

Parity BitRemember that ASCII is a seven- or eight-bit code. What about that eighth bit? It’scalled the parity bit. A parity bit is addedto the ASCII character to verify theaccuracy of the first seven bits. We aredeclaring that the number of 1s in the 8-bit character frame will be either alwaysodd or always even.

This way we can detect a single error inthe seven-bit group. Take a look at therepresentation of the transmitted uppercase “W.” In this case we have selected“odd” parity. The number of 1s in thefirst seven bits, plus the parity bit, mustalways total an odd number. The totalnumber of 1s in the binary character1010111 (W) is 5, already an odd number.Thus our parity bit will be a 0.

If we were transmitting the lower case “w”(binary 1110111), the parity bit would bea 1 because the total number of 1’s in thecharacter frame is 6, an even number.Adding the parity bit makes it odd, andconsistent with the odd parity rule.If a noise spike came onto the data line andchanged the signal voltage level enough toreverse a 1 to a 0 in the character frame, thereceiver would detect that error. The totalnumber of 1s would be even and a violation ofthe odd-parity rule.

At Watlow, we use odd, even and no parity.Odd parity sets the parity bit to 0 if there are anodd number of 1s in the first seven bitsEvenparity sets the parity bit to 0 if there are an evennumber of 1s in the first seven bits.No parity ignores the parity bit.

ASCII Control Codes, the first 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 downthe keyboard control key while pressing the appropriate keyboard key will send these values.


Start and Stop BitsA start bit informs the receiving devicethat a character is coming, and a stop bittells it that a character is complete. Thestart bit is always a 0. The stop bit isalways a 1.

The human speech equivalent of these bitscould be a clearing of the throat to getsomeone’s attention (start bit); and apause at the end of a phrase (stop bit).Both help the listener understand themessage.

Baud RateThe baud rate refers to the datatransmission. When a change in signalrepresents one data bit, baud rate is equalto bits per second (bps). Standard baudrates for computers are 300, 600, 1200,2400, 4800, 9600 and 19200 baud.

Computer LanguagesComputer languages are simply sets ofsymbols and rules for their use. There aremany computer languages and a widevariety of applications for them.Programmers use languages to enablecomputers to do real work.

SyntaxSyntax for a natural language dictates howwe put words together to make phrases andsentences. In data communications,syntax also dictates how we order the partsof a message.


Chapter Three -Watlow ControlsApproach to DataCommunicationsInterface StandardsAn interface is a means for electronicsystems to interact. It’s a specific kind ofelectrical wiring configuration. Fourinterfaces are commonly used:

EIA-232 (Full Duplex)An EIA-232 (formerly RS-232) interfaceuses three wires: a single transmit wire; asingle receive wire; and a common line.Only two devices can use an EIA-232interface. A -3 to -24 volt signal indicatesa 1 and a +3 to +24 volt signal indicates a0. The EIA-232 signal is referenced tothe common line rather than to a separatewire, as in EIA-485 and EIA-422. AnEIA-232 cable is limited to 50 feet, due tonoise susceptibility.

EIA-422 (Full Duplex)The EIA-422 interface uses five wires: a“talk” pair; a “listen” pair; and a commonline. It can handle one master and up toten remote devices in a multidrop (morethan one controller shares the same wires)network up to 4,000 feet long. EIA-422uses the difference in voltage between thetwo wires to indicate a 1 or a 0 bit. A 1 isa difference of -5 volts, while a 0 is adifference of +5 volts.

EIA-423 (Full Duplex)An EIA-423 interface is compatible withEIA-232. It is a newer standard designedfor more speed and distance. It uses threewires: a single transmit wire; a singlereceive wire; and a common line. Onlytwo 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. TheEIA-423 signal is referenced to the

common line rather than to a separatewire, as in EIA-485 and EIA-422. AnEIA-423 cable is limited up to 4,000 feet,due to noise susceptibility.

EIA-485 (Half Duplex)An EIA-485 interface uses three wires: aT+/R+, a T-/R- and a common line. A -5-volt signal is interpreted as a 1, a +5-voltsignal as a 0. As many as 32 remotedevices can be connected to a master on amulti-drop network up to 4,000 feet long.

WiringMost PCs and some PLCs have a standardEIA-232 port (usually referred to as RS-232). In these instances, you must use aninterface converter to connect to EIA-422 or EIA-485. These interface standardsare required to have a multi-drop system(more than one controller on the bus). Seethe list below for some vendors who sellthese converters.

Should your PC or PLC have theappropriate interface, just connect usingthe wiring diagram supplied with yourcontroller.

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- whilethe “B” terminal connects to the T+/R+of the controller.

The standards do not specify the wire sizeand type. Use of AWG 24 twisted pairprovides excellent results. If shielded cableis used, terminate the shield at one endonly.

Always follow the manufacturer’sinstructions supplied with the interfaceconverter. See Biasing of Buses next.

Biasing of BusesThe EIA-485 standard requires the bus tobe biased for reliable communication. Thismeans to provide termination resistors


across the T+/R+ and T-/R- wires. Oneresistor is placed at the PC or PLC whereit connects to the EIA-485 bus. Thesecond resistor is placed at the lastcontroller on the network. Do not placeresistors at each controller. Theimpedance of the wires used for the busdetermines the resistor value. For twistedpair, the value is typically 120 ohms. Inaddition, it may be necessary to have apull-up and pull-down resistor between thepower supply and ground of the interfaceadapter. Check the documentation thatcame with your interface adapter.

Biasing the bus reduces reflection of signalssent down the bus. These reflections aresometimes referred to as a standing wave.This condition is most notable whencommunicating at high baud rates.

Interface ConvertersThe purpose of an interface converter isto allow two different buses to beconnected. Interface converters arerequired when connecting an EIA-232 portto an EIA-422 or EIA-485 bus.

The EIA-422 bus is a full duplex bus. Thismeans that it can send and receive data atthe same time. The EIA-485 bus is a halfduplex bus. This means that it can onlysend or receive data at any given time.Some interface converters on the markethave provided the ability to have fullduplex with the EIA-485 bus. This isaccomplished by using two receivers andtransmitters tied in tandem. This type ofconverter will not work with the Watlowcontrollers. Be sure that the model youpurchase is designed for half duplex.

Another consideration when usinginterface converters is how the converterhandles switching between transmit andreceive. When connecting between anEIA-232 and an EIA-485, the convertermust convert two items. First it mustconvert the voltage level. Second it mustconvert from half duplex to full duplex.

This is not an easy task. Typically it isaccomplished via a handshake line from

the PC or PLC. When data flows into theconverter from the PC, a handshake line isplaced high. When data flows out of theconverter to the PC, the handshake line isplaced low. In this way, the handshake linecontrols the direction of information.Another method of achieving this is to usea built-in timer. The converter switches totransmit when a character is sent to itfrom the PC. After a period of time whenthe PC has not transmitted, the converterswitches to a receive mode.

It is important that you understand howyour converter accomplishes this task.You are required to wire this feature ormake settings on the converter to enablethis function. The PC will not talk to thecontrollers correctly with out properlysetting this.

Your converter may also require settingsthrough dip switches, to set upcommunications parameters like baud rate,data bits, start bits, stop bits andhandshaking. See the documentation thatcomes with your converter for moredetail.

The converter may require a separatepower supply. Some converters get theirpower from the handshake lines of the PC.If you rely on this method, you will needto wire these additional lines. In addition,your software must set these lines high. Amore reliable method is to use the externalpower supply. This is especially necessarywhen using a laptop computer.

ProtocolsProtocol describes how to initiate anexchange. It also prevents two machinesfrom attempting to send data at the sametime. There are a number of different datacommunications protocols, just as thereare different human cultural protocols thatvary according to the situation.

The protocol part of Watlowcommunications is very important,because it gives us a quality ofcommunication that others often don’thave. Protocol-driven communications


are more accurate, because they are lessprone to both operator and noise errors.Protocol maintains system integrity byrequiring a response to each message. It’slike registered mail — you know that yourletter has been received because the postoffice sends you a signed receipt.

In Watlow data communications, a dialogwill continue successfully as long as themessages are in the correct form andresponses are returned to the protocolleader. If the operator enters an incorrectmessage, or interference comes on to thedata line, there will be no response. Inthat case the master must retransmit themessage or go to a recovery procedure. Ifan operator continues to enter anincorrect message or interferencecontinues on the data line, the system willhalt until the problem is resolved.Watlow provides you with three protocolchoices: XON/XOFF, ANSI x3.28, ModbusRTU

XON/XOFFThe first protocol is conventionalXON/XOFF protocol. It works very wellfor systems that do not require a messageresponse and for those with only twodevices (one PC and one controller).Sending of the "XON" (0x11) and "XOFF"(0x13) controls information. This is thesimplest protocol offered by WatlowControls.

ANSI x3.28The second, called “Full Protocol,” isbased on the American National StandardInstitute’s standard ANSI X3.28-1976,Subcategory 2.2. The Full Protocol isrequired for systems that need a responseto every message, and for any “multi-drop” network, which has more than twocommunication devices. Addressing acertain controller on the bus, thenenclosing all messages with a <STX> startof text (0x02) and <ETX> end of text(0x03) controls information exchange.The characters <ENQ>, <EOT>, <DLE>are used to determine who has control ofthe bus. Lastly, all messages are <ACK>

acknowledged (0x06) or <NAK> negativeacknowledged (0x15) to ensure messageswhere received correctly.

Modbus Remote Terminal Unit(RTU)Gould Modicon, now called AEGSchneider, created the third protocol forprocess control systems called "Modbus".This protocol is the most complex of thethree. It has the advantage of beingextremely reliable in exchanginginformation, a highly desirable feature forindustrial data communications. Thisprotocol works on the principle of packetexchanges. The packet contains theaddress of the controller to receive theinformation, a command field that sayswhat is to be done with the informationand several fields of data. Reading fromthese registers retrieves all information inthe controller. These registers are listed inyour user’s manual. You will need this listto determine where the data is located.The last item sent in the packet is a fieldto ensure the data is received intact. Thisis called a cyclic redundancy check-sum.All information exchanged is in hexnumbers. Watlow only supports the binaryversion of Modbus, referenced as RTU.The ASCII version is less efficient and isnot supported.


Chapter Four -Human MachineInterfaces (HMI)HMI stands for Human-Machine-Interface, and is sometimes referred to asMan-Machine-Interface (MMI). This is anoperator interface that allows you tomonitor and control your process. Manysoftware packages were written to allow aPC to perform this function. Use care inselecting software packages. Some will runonly under a specific disk operating systemsuch as Windows NT from Microsoft. Theserial interface and protocol must matchbetween the PC or PLC and the controller.Many companies provide free workingdemonstration copies. Obtain ademonstration copy so you can see if theprogram meets your needs.

Listed below are a few of the manysoftware packages that claim to supportthe Modbus protocol. Watlow does notrecommend any one software package norsupports the implementation of anysoftware package not sold by Watlow.Contact the software manufacturer formore information in applying theirsoftware.

Write your own HMI

Writing an XON/XOFFApplicationThe great thing about XON/XOFFprotocol is the simplicity ofcommunications. The basic structure is tosend information to the controller asneeded until you receive an XOFF (0x13).You must wait until you receive an XON(0x11) before continuing. The controllerfollows this same scheme. There are noconfirmations of commands sent. Thisprotocol is highly efficient in that fewcharacters are sent to handle the flow of

information. This protocol is sometimesreferred to as “flow control”.The disadvantage of this protocol is lowerreliability in ensuring that both partiesreceive the proper information. Inaddition, only two devices can be on a busbecause no means is provided to addressany controller.

Handling Error Codes (ER2) All communications' related error codesare ER2 error codes, which means thatthey're not considered cause for ashutdown of the unit itself. WithXON/XOFF flow control, error codes maybe generated, but there will be no standardindication of this fact. Therefore, youmay want to query the status of ER2 aftereach command sent to see if it wassuccessful.

User ResponsibilityUsers must refrain from altering promptsthat do not appear on the controller’sfront panel or are not included on thespecific model. For example, do not sendan A2LO command to a unit not equippedwith an alarm for output 2.Most Watlow controllers contain aregister to disable saving of the current setpoint to EEPROM. When using your PCor PLC to control the set point in theWatlow controller, the EEPROM may beprematurely damaged. There is a limit tothe number of times you can storeinformation in the EPPROM. PCs canquickly reach this limit if the set point iscontinually changed, as in a rampingcontroller. Disabling this feature willprevent this damage.

Care must also be taken that the processcan not cause damage to property orinjury to personnel if the wrongcommands are sent due to operator erroror equipment malfunction. Be sure to uselimit devices on the equipment to preventsystem runaway.

Writing an ANSI x3.28 ApplicationHandling Error Codes (ER2)All communications' related error codesare ER2 error codes, which means that


they're not considered cause for ashutdown of the unit itself. There isalways a communications error codegenerated when the <NAK> character(0x15) is sent under the ANSI x3.28protocol

User ResponsibilityUsers must refrain from altering promptsthat do not appear on the controller’sfront panel or are not included on thespecific model. For example, do not sendan A2LO command to a unit not equippedwith an alarm for output 2.

Most of Watlow controllers contain aregister to disable saving of the current setpoint to EEPROM. When using your PCor PLC to control the set point in theWatlow controller, the EEPROM may beprematurely damaged. There is a limit tothe number of times you can storeinformation in the EPPROM. PCs canquickly reach this limit if the set point iscontinually changed, as in a rampingcontroller. Disabling this feature willprevent this damage.


Because of the wide array of choicesavailable for setting up a Watlowcontroller, only a subset of the promptscontains parameters in a given situation.The user's manual explains theinterrelations between prompts.

Writing a Modbus ApplicationModbus RTU enables a computer or PLCto read and write directly to registerscontaining the controller’s parameters.With it you could read all 141 of thecontroller’s parameters with five readcommands.

Because of the wide array of choicesavailable for setting up a controller

utilizing Modbus, only a subset of theprompts contain parameters in a givensituation. This document explains theinterrelations between prompts.

If you already have a software applicationthat uses Modbus, you can simply skip tothe Temperature/process ControllerPrompt Table or the Modbus RTU AddressTable in the user’s manual for the addressinformation your program will need. Therest of this section on the Modbusprovides information for writing asoftware 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 bewritten in twos' complement format.Parameters are stored in two-byteregisters accessed with read and writecommands to a relative address.

3. Messages are sent in packets that aredelimited by a pause at least as long asthe time it takes to send 30 bits. Todetermine this time in seconds, divide30 by your baud rate.

4. Because changing some parametersautomatically changes or defaultsother parameters, use the CompleteParameter Download Sequence tablelisted in the user's manual to orderwrite commands.

Using a controller address of 0x00 for awrite command, will send thatcommand to all the controllers in thenetwork. This is a powerful feature if allthe controllers on a network use all ormost of the same parameters.

Packet format: nn | nn | nnnn… | nnnn

addresscommandregisters and/or dataCRC


Packet SyntaxEach message packet begins with a one-byte controller address, from 0x01 to 0xF7.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 RedundancyChecksum (CRC) for error detection.

Read Multiple Registers Command (0x03 or 0x04)This command returns from 1 to 32 registers.

Packet sent to controller:| nn | 03 | nn nn | 00 nn | nn nn |

controller address (one byte)read command (0x03 or 0x04)starting register high bytestarting register low bytenumber of registers high byte (0x00)number of registers low byteCRC low byteCRC high byte

Packet returned by controller: | nn | 03 | nn | nn nn … nn nn | nn nn |

controller address (one byte)read command (0x03 or 0x04)number of bytes (one byte)first register data low bytefirst register data high byte……register n data high byteregister n data low byteCRC low byteCRC high byte


Example (988 only): Read register 0 (model number) of the controller at address 1.Sent: 01 03 00 00 00 01 84 0AReceived: 01 03 02 03 DC B9 2DMessage: 988 (0x03DC).

Example (988 only): Read register 1 and 2 (Process 1 and 2 values) of controller ataddress 5.Sent: 05 03 00 01 00 02 94 4FReceived: 05 03 04 00 64 00 C8 FF BAMessage: 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 backthe command. An attempt to write to a read-only parameter returns an illegal dataaddress error (0x02). (See “Exception Responses,” pg. 4.9.)

Packet sent to controller:| nn | 06 | nn nn | nn nn | nn nn |

controller address (one byte)write to a register command (0x06)register high byteregister low bytedata high bytedata low byteCRC low byteCRC 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 D5Received: 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 towrite to a read-only parameter returns an illegal data address error (0x02). (See“Exception Responses,” pg. 4.9.)

Packet sent to controller:| nn | 10 | nn nn | 00 01 | 02 | nn nn | nn nn |

controller address (one byte)write to multiple registers command (0x10)starting register high bytestarting register low bytenumber 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 bytedata low byteCRC low byteCRC high byte


Packet returned by controller: | nn | 10 | nn nn | 00 01 | nn nn |

controller address (one byte)write to multiple registers command (0x10)starting register high bytestarting register low bytenumber of registers to write high byte (0x00)number of registers to write low byte (must be 0x01)CRC low byteCRC high byte

Loop Back Command (0x08)This command simply echoes the message. This serves as a quick way to checkyour wiring.

Packet sent to controller:| nn | 08 | nn nn | nn nn |

controller address (one byte)loop back command (0x08)data high bytedata low byteCRC low byteCRC high byte

Example: Run loop back test on controller at address 40 (0x28).Sent: 28 08 55 66 77 88 31 B7Received: 28 08 55 66 77 88 31 B7

Exception ResponsesWhen a controller cannot process a command it returns an exception response andsets the high bit (0x80) of the command.0x01 illegal command0x02 illegal data address0x03 illegal data value

Packet returned by controller: | nn | nn | nn | nn nn |

controller address (one byte)command + 0x80exception code (0x01 or 0x02 or 0x03)CRC low byteCRC high byte


Messages with the wrong format, timing or CRC are ignored. A read command sentto an inactive parameter returns 0x0000.

Example: Exception 01 - Command 02 is not supported.Sent: 01 02 00 01 00 02 A8 0BReceived: 01 82 01 81 60

Example: Exception 02 - The parameter at register 45 (0x002D) is inactive.Sent: 01 06 00 2D 00 01 D8 C3Received: 01 86 02 C3 A1

Example: Exception 03 - Cannot write 12,000 (0x2EE0) to register 7, out of range,illegal data value.Sent: 01 06 00 07 2E E0 24 23Received: 01 86 03 02 61

Special Modbus FunctionsThe 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.


Handling Error CodesError codes are divided into two types.Read error codes and write error codes arecalled exception codes. Reading from aregister that does not exist or is currentlydisabled will typically respond with a largeout of range value such as -32000, -32001,or -32002. The Series 988 returns a valueof zero.

Writing to a register that is not supported,is inactive or out of range will return apacket with 0x80 added to the commandsent. The byte following this will containthe value 0x01 for illegal command, 0x02for illegal address, or 0x03 for illegal datavalue. Writing to a read only register willreturn an exception code 0x02.See your user's manual for exact values anddefinitions.

User ResponsibilityUsers must refrain from altering promptsthat do not appear on the controller’sfront panel or are not included on thespecific model. For example, do not sendan A2LO command to a unit not equippedwith an alarm for output 2.

Most of Watlow controllers contain aregister to disable saving of the current setpoint to EEPROM. When using your PCor PLC to control the set point in theWatlow controller, the EEPROM may beprematurely damaged. There is a limit tothe number of times you can storeinformation in the EPPROM. PCs canquickly reach this limit if the set point iscontinually changed, as in a rampingcontroller. Disabling this feature willprevent this damage.


Purchase an HMI packageNot all HMIs are equal in performance. Setup and operation / function of each

manufacturer’s HMI package is unique.Industrial controllers operate in a harsh,electrically noisy environment. This cancause less robust HMIs to workintermittently or not at all. In addition,the platform (PC or PLC) which runs theHMI is subject to failures causingunpredictable operation of your process.Watlow has not tested the HMIs listedwith the exception of ANAWIN andWATLINK. This list is provided asinformational only. Watlow makes noclaims as to the performance orcompatibility with any HMI softwarepackage.

Anawin by Watlow Anafaze334 Westridge DriveWatsonville, CA 95076Phone 408-724-3800http://www.watlow.com

WATLINK by Watlow Controls1241 Bundy BlvdWinona, MN 55987Phone 507-454-5300http://www.watlow.com

CONTROLWARE by Controlware245 Northland BlvdCincinnati, OH 45246-3603Phone 800-776-9704http://www.controlware.com

Cimplicity by GE FanucPhone 1-800-648-2001http://www.gefanuc.com

Genesis by Iconics100 Foxborough BlvdFoxborough, MA 02035Phone 800-946-9679http://www.iconics.com


Interact by CTC50 W. TechneCenter DriveMilford, OH 45150Phone 513-831-2340http://www.ctcusa.com

KEPware MMI by KEPware, Inc.81 Bridge StreetYarmouth, ME 04096Phone 207-846-5881http://www.kepware.com

LabView by National Instruments6504 Bridge Point ParkwayAustin, TX 78730-5039Phone 512-794-0100http://www.natinst.com

Lookout by National Instruments6504 Bridge Point ParkwayAustin, TX 78730-5039Phone 512-794-0100http://www.natinst.com

Modbus for Windows by CaltaComputer Systems Ltd.

230, 550-71 Ave. SECalgary, Alberta Canada T2H 0S6Phone 403-252-5094http://www.calta.com

OI-2000 by Software Horizons, Inc.10 Tower Office ParkSuite 200Woburn, MA 01801-2120Phone 617-933-3747http://www.shorizons.com

SpecView by SpecView, LLC41 Canyon Green CourtSan Ramon, CA 94583Phone 510-275-0600http://www.specview.com

Visual Logic Controller by SteeplechaseSoftware, Inc.

1330 Eisenhower PlaceAnn Arbor, MI 48108Phone 313-975-8100http://www.steeplechase.com

Wonderware 2000 by WonderwareCorp.

100 Technology DriveIrvine, CA 92718Phone 714-727-3200http://www.wonderware.com


Chapter Five -Operator InterfacePanelsNot all Operator Interface Panels are equalin performance. Programming of eachmanufacturer’s panel is unique. Industrialcontrollers operate in a harsh, electricallynoisy environment. This can cause lessrobust panels to work intermittently ornot at all. Watlow has not tested thepanels listed and this list is provided asinformational only. Watlow makes noclaims as to the performance orcompatibility with any Operator InterfacePanel.

EXOR4740T Interstate DriveCincinnati, OH 45246Phone 513-874-4665http://www.exor-rd.com

CTC50 W. TechneCenter DriveMilford, OH 45150Phone 513-831-2340http://www.ctcusa.com

Maple Systems1930 220th Street SESuite 101Bothell, WA 98021Phone 425-486-4477http://www.maple-systems.com

AdvantechPhone 1-800-800-6889http://www.advantech-usa.com

Interface AdaptersNot all converters are equal inperformance. Industrial controllers

operate in a harsh, electrically noisyenvironment. This can cause less robustconverters to work intermittently or notat all. Watlow has not tested theconverters listed and this list is provided asinformational only. Watlow makes noclaims as to the performance orcompatibility with any converter.

B&B Electronics707 Dayton RoadPO Box 1040Ottawa, IL 61350Phone 815-433-5100http://www.bb-elec.com

Part # 485OIC for EIA-232 to EIA-422or EIA-485

Dataforth Corporation (formerlysupplied by Burr-Brown)

3331 E. Hemisphere LoopTucson, AZ 85706Phone 800-444-7644Part # LDM422 for EIA-232 to EIA-422Part # LDM485 for EIA-232 to EIA-485

CMC – Connecticut MicrocomputerCorporation

Watlow Software Tools

920Comm DiagnosticSoftwareWatlow has a program available free ofcharge called “920COMM.EXE” that isused with the Series 920 Controller. Thiscan be downloaded from our BBS at 507-452-3958. This is a terminal program thathandles the protocol for you. Theprogram can be used to determine if yourcables are properly connected and that thecontroller is working. This programsupports the ANSI x3.28 and XON/XOFFprotocols.


922Comm DiagnosticSoftwareAnother program available free of chargeis called “922COMM.EXE" which is usedwith the Series 922 Controller. This can bedownloaded from our BBS at 507-452-3958. This is a terminal program thathandles the protocol for you. Theprogram can be used to determine if yourcables are properly connected and that thecontroller is working. This programsupports the ANSI x3.28 and XON/XOFFprotocols.

Comm4 Diagnostic SoftwareThe “COMM4.EXE” program can bedownloaded free of charge from our BBS at507-452-3958. This is a terminal programwhich handles the protocol for you. Theprogram can be used to determine if yourcables are properly connected and that thecontroller is working. This programsupports the ANSI x3.28 and XON/XOFFprotocols.

Comm5vb DiagnosticSoftwareThe “COMM5VB.EXE” program can bedownloaded free of charge from our BBS at507-452-3958. This is a terminal programthat handles the protocol for you. Theprogram can be used to determine if yourcables are properly connected and that thecontroller is working. This programsupports the Modbus, ANSI x3.28 andXON/XOFF protocols.

CRC

Cyclical Redundancy Checksum (CRC)AlgorithmThis C routine, calc_crc(), calculates thecyclical redundancy checksum, CRC, for astring of characters. The CRC is the resultof dividing the string by 0xA001. Modbusapplications calculate the packet’s CRCthen append it to the packet.

#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 = 0xffff;/* Loop through the entire packet */do{/* Exclusive-OR the byte with the CRC */crc ^= (unsigned int)*char_ptr;/* Loop through all 8 data bits */bit_count = 0;do{

/* If the LSB is 1, shift the CRC and XORthe polynomial mask with the CRC */if(crc & 0x0001){crc >>= 1;crc ^= POLYNOMIAL;

}

/* If the LSB is 0, shift the CRC only */else{crc >>= 1;

}} while(bit_count++ < 7);} while(char_ptr++ < end_of_packet);return(crc);}


SummaryAs first stated in this article, the steps involvedto communicate are:

1. Determine how many controllers youwill communicate with

2. Pick a protocol and interface thatsupports the information exchange

3. Purchase hardware and software to makethis happen.

The number of controlled zones will determinethe number of controllers connected to the PC orPLC. Pick a protocol that will support thisnumber. Consider speed and reliability ofcommunications when picking the protocol. Askyourself, how will the devices understand eachother? Pick an interface that will support thenumber of devices connected, transmit over thedesired distance and is industrially hardened(will communicate in electrically noisyenvironments). Lastly, purchase an interface,controllers, PC or PLC and software that willwork together. Software may be written toaccomplish the task if you have the skills andresources to do so.

Interface ComparisonInterface Maximum Max # Cable Voltage Balanced/ Duplex

Standard Bus Length Controllers Type Level UnbalancedEIA-232 50 feet 1 3-wire 3 – 24 v Unbalanced Full

EIA-423 4,000 feet 1 3-wire 3 – 12 v Unbalanced Full

EIA-422 4,000 feet 10 5-wire 2.0 – 6 v Balanced Full

EIA-485 4,000 feet 32 3-wire 1.6 – 6 v Balanced Hal


Appendix

Glossary

AddressA unique designator for a location of dataor a controller that allows each location orcontroller on a single communications busto respond to its own message. Similar toyour own residence address.

ANSIA merican N ational S tandards I nstitute

ANSI x3.28The American National Standards Institutedeveloped this communication standardprotocol. This method uses a uniqueaddress for each device. Only the mastercan initiate a communications session bysending an address and then the <ENQ>character. All other messages must startwith a start of text <STX> and end with anend of text <ETX> character. The bus isreleased to the other device by sending<EOT> character. Messages are <ACK>acknowledged or <NAK> negativeacknowledged.

ASCII (pronounced AS-KEY)American Standard Code for InformationInterchange. A universal standard forencoding alphanumeric characters into 7or 8 binary bits.

AsynchronousCommunications where characters can betransmitted at an unsynchronized point intime. In other words, it can start and stopanytime. The time between transmittedcharacters may be of varying lengths.Communication is controlled by “start”and “stop” bits at the beginning and end ofeach character.

BaudUnit of signaling speed derived from the numberof events per second (normally bits per second).

Baud rateThe rate of information transfer in serialcommunications, measured in bits per second.

BinaryNumber based system where only two charactersexist, 0 and 1. Counting is 0, 1, 10, 11...

BitDerived from “ BI nary Digi T ”, a one or zerocondition in the binary system.

ByteA term referring to eight associated bits ofinformation, sometimes called a “character”.

CAN BusThe C ontroller A rea N etwork Bus is a serialcommunications protocol that includes softwareand hardware. CAN was originally developed bythe German company Robert Bosch for use in theauto industry to provide a cost-effectivecommunications bus for in-car electronics.

CharacterLetter, numeral, punctuation, control figure orany other symbol contained in a message.Typically this is encoded in one byte.

CommunicationsThe use of digital computer messages to linkcomponents. (See serial communications andbaud rate)

ConverterThis device will convert from one hardwareinterface to another such as from EIA-232 to EIA-485. The converter may be transparent to thesoftware, which means you do not have to giveany special considerations to softwareprogramming.

CRCWhen data is corrupted during transmission, amethod is used to return the data to its correctvalue. This can be accomplished through severalmethods: parity, checksum and CRC (cyclicredundancy checksum) are three of these. C yclicR edundancy C hecksum is an error-checkingmechanism using a polynomial algorithm basedon the content of a message frame at thetransmitter and included in a field appended tothe frame. At the receiver, it is then comparedwith the results of the calculation that isperformed by the receiver.


DataThe information that is transferred acrossthe communications bus. This may be asetpoint, setup parameter, or anycharacter. This information is transferredto an address or register.

DB-9A standardized connector shaped like theletter “D” when viewed on edge. Thisconnector has 9 contacts. It is utilized onmost IBM AT compatible PCs as the serialport.

DB-15A standardized connector shaped like theletter “D” when viewed on edge. Thisconnector has 15 contacts. It is utilizedon most IBM AT compatible PCs as thegame/midi port.

DB-25A standardized connector shaped like theletter “D” when viewed on edge. Thisconnector has 25 contacts. It is utilizedon most IBM AT compatible PC’s as theparallel port when the PC end containssocket contacts. Can also be the serial portwhen the PC end contains pin contact.

DecodeThis is the reverse of encode. When apiece of data has information embedded init, decode is to extract that information.Ex. To extract an “A” from 01000001.

DeviceNetA software protocol / hardware interfacebased on CAN. A low cost communicationlink that connects industrial devices over anetwork. Uses twisted pair wires for thepower and bus. Nodes can be removed orinserted on the bus without powering downthe network.

Double WordEquivalent to two words or four bytes.This equals 32 bits.

DuplexThe ability to send and receive data at thesame time. “To listen and talk at the sametime.”

EIASee Electronic Industries Association

EIA-232Electronic Industries Associationdeveloped this standard hardware interfaceto allow one device to talk to anotherdevice in full duplex mode. This methoduses a differential voltage between onewire and ground. Also called an unbalancedsystem since the ground wire carries thesum of current of all lines. First standardto gain wide acceptance by manufacturers.Transmission is limited to about 50 feet.

EIA-422Electronic Industries Associationdeveloped this standard hardware interfaceto allow up to 10 devices to be on a bus atone time. This method uses a differentialvoltage between two wires. Also called abalanced system since each wire carries thesame current values. This has theadvantage of being immune to outsideelectrical disturbances.

EIA-423Electronic Industries Associationdeveloped this standard hardware interfaceto allow one device to talk to anotherdevice in full duplex mode. This methoduses a differential voltage between onewire and ground. Also called an unbalancedsystem since the ground wire carries thesum of current of all lines. This standard iscompatible with EIA-232. The outputswere beefed up to allow transmission up to4000 ft.

EIA-485Electronic Industries Associationdeveloped this standard hardware interfaceto allow up to 32 devices to be on a bus atone time. This method uses a differentialvoltage between two wires. Also called abalanced system since each wire carries thesame current value. This has the advantageof being immune to outside electricaldisturbances.

EIA/TIA -232, -422, -423 and -485Data communications standards set by theElectronic Industries Association andTelecommunications 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 establishesstandards for electronics and datacommunications

EncodeTo embed information into a piece ofdata. This is the reverse of decode. Ex.Let’s let 01000001 stand for an “A”.

Error CorrectionWhen an inconsistency is in the data, amethod is used to detect and/or return thedata to its correct value. This can be donethrough several methods, parity, checksumand CRC (cyclic redundancy checksum) area three of these.

EthernetA local area network developed by Xeroxin the early 70’s and standardized byXerox, Digital Equipment and Intel in1978. This is a serial communicationsmethod which all devices share the lines.An address is sent in a packet to talk to adevice on the line. This protocol supportspeer-to-peer communications.

EvenThis term is used with parity. See parity.

FieldbusThe term fieldbus is a general definitionfor an industrial network media thatresides at the machine level and below in atotal network system. The primarypurpose of this network is to interconnectthe machine level and sublevel controlfunctions and services in a distributivetopology. It is not a particular protocol orphysical connection system. Included inthis generalization definition are standardprotocols of Profibus, Modbus, DeviceNet,SDS, WorldPIP, and P-Net.

FirmwareInstruction or data stored in an IC(integrated circuit) or on a read only disk.

This data is programmed once and cannoteasily be changed as software can.

FullSee Full Duplex.

Full DuplexFull is used to mean the duplex’s fullcapability. The ability to send and receivedata at the same time. The same as duplex.

GPIBSee IEEE488

Half DuplexThe ability to send or receive data, but notat the same time. “To listen or talk, butnot both at the same time.”

Handshake (Handshaking)Exchange of predetermined signalsbetween two devices establishing aconnection. Using extra wires or softwaresignals to coordinate communications,signals can be sent to tell the transmitterthe current status of the other devicereceiver. Ex. Are you busy or are youready?

Hex or HexadecimalNumber based system where sixteencharacters exist, 0 to 9, A to F. Countingis 0..9,A,B,C..

HMIHuman to Machine Interface typicallyperformed in software on a personalcomputer. Also called MMI.

IEEE488Bus developed by Hewlett-Packard in 1965as HP-IB. Also referred to as GPIB(General Purpose Interface Bus). Consistof 8 data lines and 8 control lines. Buslength limited to 20.0 meters. Supports 15devices on the bus at one time.

Logic LevelA voltage measurement system where onlytwo stable voltage values exist. Ex. 0v and5V, or -3v and +3v.


MarkRepresents the transmission of data bitlogic 1 (see logic level). Usually this is themost negative voltage value in serialcommunications.

MasterThe device on the bus that controls allcommunications. Only the master caninitiate conversation.

ModbusA software protocol developed by GouldModicon (now AEG) for process controlsystems. No hardware interface is defined.Modbus is accessed on the master/slaveprinciple, the protocol providing for onemaster and up to 247 slaves. Only themaster can initiate a transaction. This is ahalf duplex protocol.

MMIMan to Machine Interface typicallyperformed in software on a personalcomputer. Also called HMI.

NetworkWhen two or more devices sharecommunications lines, the devices are“networked”.

NodeA point of interconnection to a network.

Noise ImmunityThe ability of communications lines toignore electrical noise generated in thecommunications lines by nearby magneticand electrostatic fields.

OddThis term is used with parity. See parity.

OSIOpen Systems Interconnection are thosewhich conform to specifications andguidelines that are open to all. This allowsequipment from any manufacturer, whichclaims to comply with the standard, to beused interchangeably on the standardnetwork.

ParallelCommunication using this method,transfers eight bits or one byte at a timeover eight data wires and one ground wire.This method is eight times faster thanusing serial but utilizes more hardware.

ParityA bit is assigned at the beginning of a byteto stand for parity. When the ‘1’ bits arecounted, the number will be even or odd.A parity bit is used to ensure that theanswer is always even if even parity or oddif odd parity. If the receiving end countsthe ‘1’ bits and the sum is not the sameodd or even, an error is generated. Ex.00010000 has an odd number of 1s. Ineven parity, we would set the parity to 1so we have an even number of bits. In oddparity, we would set the parity bit to 0 sowe have an odd number of ‘1’ bits. Parityis used to detect errors caused by noise indata transmission.

PCPersonal Computer, coined by IBM whenit introduced its first IBM PC Jr., whichlater became PC, XT, AT, 286, 386, 486,Pentium, Pro, MMX Pentium, and latestPentium II.

Peer to PeerTwo devices that can talk to each other.Both devices can initiate communications.This may also be called Master-to-Mastercommunications.

ProfibusProfibus is actually three buses. ProfibusFMS (Field Message Specification),Profibus PA (Process Automation), andProfibus DP (Process Periphery). FMS is ahigher level bus intended to operate withPLCs, Pcs and higher level nodes. ProfibusDP supports three masters. The mastersthen operate with field nodes as master-to-slaves. Profibus PA is an intrinsically safebus. The protocol is essentially the sameas DP but the electrical / physicalspecifications are modified to satisfy lowvoltage and current requirements.


ProtocolA set of rules for communication. Thiswill specify what method to transferinformation, packet size, informationheaders and who should talk when. It isused to coordinate communicationactivity.

ReceiveTo accept data sent from another device.The device that receives the data is thereceiver.

RegisterAn area of memory that providestemporary storage of digital data.

RJ11A connector used on most telephones thathas four terminals.

SDSSmart Distributed System is a CAN baseddevice-level control network that can bescan or event driven, configured as master-slave or peer-to-peer, and can supportdevices of varying complexity. . Usestwisted pair wires for the power and bus.

SlaveA device that only responds to commands.This device never starts communicationon it’s own. Only the Master can do this.(See Master)

SCADASupervisory Control and Data Acquisition

SerialTo process something in order. First item,second item, etc.

Serial CommunicationsA method of transmitting informationbetween devices by sending all bits serially(see serial) over a single communicationchannel.

EIA/TIA-232(Formerly RS-232) -An Electronic Industries Association(EIA)/Telecommunication IndustryAssociation (TIA) standard for interface

between data terminal equipment and datacommunications equipment for serialbinary data interchange. This is usually forcommunications over a short distance (50feet or less) and to a single device.

EIA/TIA-485 (Formerly RS-485) –An Electronic Industries Association(EIA)/Telecommunication IndustryAssociation (TIA) standard for electricalcharacteristics of generators and receiversfor use in balanced digital multi-pointsystems. This is usually used tocommunicate with multiple devices over acommon cable or where distances over 50feet are required.

SoftwareInformation of data or program stored inan easily changeable format. (RAM,Floppy Disk, Hard Disk)

SpaceRepresents the transmission of a data bitlogic 0 (see logic level). Usually this is themost positive voltage value in serialcommunications.

Start BitA binary bit or logic level that representswhen the serial data information is aboutto start (at the beginning of a character orbyte). This voltage level is positive.

Stop BitA binary bit or logic level that representswhen the serial data information iscomplete (at the end of a character orbyte). This voltage level is negative.

SynchronousWhen data is transmitted on a data lineand a clock signal is used on another lineto determine when to check the data linefor a logic level. This clock is said to“synchronize” the data.

TCP/IPTransmission Control Protocol/InternetProtocol is a software protocol used tosend and receive data between differentcomputer systems. Standard protocol usedon the Internet.


TransmitTo send data from one device to another.The device that sends the data is thetransmitter.

WordTwo bytes make a word. This contains 16bits.

XON/XOFFA software protocol that controls the flowof serial information. Sending an XONtells the transmitter to start sendinginformation. An XOFF tells thetransmitter to stop sending until thereceiver has processed the currentinformation. XOFF = DC3 = Control S =hex 11, XON = DC1 = Control Q = hex13.

Disclaimer of WarrantyThis is a general overview and statementof the safety-related need for andmethods of applying "data comunicationsfor temperature processes." Because ofthe diversity of conditions and hazardsunder which control products may beapplied, and because of the differences incomponents and methods of theirinstallation, no representation or warrantyof any kind, express or implied, ishereby made, that the data comunicationsdiscussed and presented herein will beeffective in any particular application orset of circumstances, or that addi-tional or different precautions will not bereasonably necessary for a parti-cular application. We will be pleased toconsult with you regarding a specificapplication upon request.

Trademark InformationWatlow®, Gordon®, Anafaze®,ANASOFT®, ANAWIN®, MICRODINare trademarks of Watlow ElectricManufacturing Company.Modbus™ is a trademark of AEGSchneider Automation.Windows® and Microsoft® are trademarksof the Microsoft Corporation.

Watlow Contro ls Communicat ions Guide 29

IndexA922 Comm Diagnostic 21Appendix 23ASCII Chart 6ASCII 5Audience 4

BBaud Rate 8Biasing of Buses 9Bits and Bytes 5

CCharacter Format 5Comm4 Diagnostic Software 21Comm5vb Diagnostic Software 21Computer Languages 8Controller Comparison Summery 22Convention 4CRC 21

DDisclaimer of Warranty 28

EElements of Machine to Machine

Comm. 5

GGetting Started 4Glossary 23

IInterface Adapters 20Interface Comparison 22Interface Converters 10Interface Standards 9

MMedia 4

PParity Bits 7Protocols 10Purchase an HMI package 18Purpose 4

SSerial Communication 7Start and Stop Bits 8Syntax 8

WWatlow Software Tools 20Wiring 9Write Your Own (HMI) 12

Watlow Controls Communications GuideWatlow Controls, 1241 Bundy Blvd., P.O. Box 5580, Winona, Minnesota USA 55987-5580,

Phone: (507) 454-5300, Fax: (507) 452-4507

How to Reach Us

Quality andMissionStatement:Watlow Controls will bethe world’s bestsupplier of industrialtemperature controlproducts, services andsystems by exceedingour customers’,employees’ andshareholders’expectations.

Contact

• 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.

WarrantyMost Watlow Controls are warranted to be free of defects in material and work-manship for 36 months after delivery to the first purchaser for use, providingthat the units have not been misapplied. Since Watlow has no control over theiruse, and sometimes misuse, we cannot guarantee against failure. Watlow'sobligations hereunder, at Watlow's option, are limited to replacement, repair orrefund of purchase price, and parts which upon examination prove to be defec-tive within the warranty period specified. This warranty does not apply to 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.• Put the RMA number on the shipping label, and also on a written descrip-

tion of the problem.• A restocking charge of 20% of the net price is charged for all standard units

returned to stock.

Your Authorized Watlow Distributor:

Documents

CAUTION - TestEquity