Data Communications Reference Electronic User’s Manual ISO 9001 Registered Company Winona, Minnesota USA 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 June 1998 Made in the U.S.A. $15.
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. information that is important for protecting you, others and equipment from damage.
T Table of Contents Chapter 1 Chapter 4 Audience . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 Write Your Own (HMI) . . . . . . . . . . . . . . . . .12 Media . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4 Purchase an HMI package . . . . . . . . . . . . .18 Purpose . . . . . . . . . . . . . . . . . . . . . . . . . . . .4 Chapter 5 Getting Started . . . . . . . . . . . . . . . . . . . . . . .4 Interface Adapters . . . . . . . . . . . . . . . . . . .20 Convention . . . . . . .
5. Configure the PC or PLC software and hardware to do what you want them to do. Chapter One Introduction 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.
Bits and Bytes Chapter 2 Definition of Terms 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. Elements of Machine-toMachine Communication In human communication there are basic words and sentences used to get a message across.
ASCII Chart ASCII Char NUL SOH STX ETX EOT ENQ ACK BEL BS HT LF VT FF CR SO SI DLE DC1 DC2 DC3 DC4 NAK SYN ETB CAN EM SUB ESC FS GS RS US SP ! “ # $ % & ‘ ( ) * + , .
Serial Communication ASCII Control Codes 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. 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. Serial contrasts with parallel communication, which sends several bits of information simultaneously over multiple lines or channels.
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 is complete. The start bit is 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 the message. Baud Rate The baud rate refers to the data transmission.
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. Chapter Three Watlow Controls Approach to Data Communications EIA-485 (Half Duplex) An EIA-485 interface uses three wires: a T+/R+, a T-/R- and a common line. A -5volt 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.
the PC or PLC. When data flows into the converter 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 is 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.
acknowledged (0x06) or negative acknowledged (0x15) to ensure messages where received correctly. 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.
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. Chapter Four Human Machine Interfaces (HMI) HMI stands for Human-MachineInterface, and is sometimes referred to as Man-Machine-Interface (MMI).
utilizing Modbus, only a subset of the prompts contain parameters in a given situation. This document explains the interrelations between prompts. they're not considered cause for a shutdown of the unit itself. There is always a communications error code generated when the character (0x15) is sent under the ANSI x3.
Packet Syntax Each 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 Redundancy Checksum (CRC) for error detection.
Example (988 only): Read register 0 (model number) of the controller at address 1. Sent: 01 03 00 00 00 01 84 0A 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.
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 byte starting register low byte number of registers to write high byte (0x00) 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.
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 00 01 00 02 A8 0B 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 (0x2EE0) to register 7, out of range, illegal data value.
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.
Interact by CTC 50 W. TechneCenter Drive Milford, OH 45150 Phone 513-831-2340 http://www.ctcusa.com Visual Logic Controller by Steeplechase Software, Inc. 1330 Eisenhower Place Ann Arbor, MI 48108 Phone 313-975-8100 http://www.steeplechase.com KEPware MMI by KEPware, Inc. 81 Bridge Street Yarmouth, ME 04096 Phone 207-846-5881 Wonderware 2000 by Wonderware Corp. 100 Technology Drive Irvine, CA 92718 Phone 714-727-3200 http://www.wonderware.com http://www.kepware.
operate in a harsh, electrically noisy environment. This can cause less robust converters to work intermittently 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. Chapter Five Operator Interface Panels Not all Operator Interface Panels are equal in performance. Programming of each manufacturer’s panel is unique.
#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; 922Comm 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 507-4523958. This is a terminal program that handles the protocol for you.
Interface Comparison Interface Standard EIA-232 EIA-423 EIA-422 EIA-485 Maximum Bus Length 50 feet 4,000 feet 4,000 feet 4,000 feet Max # Controllers 1 1 10 32 Cable Type 3-wire 3-wire 5-wire 3-wire Summary As first stated in this article, the steps involved to communicate are: 1. 2. 3. Determine how many controllers you will communicate with Pick a protocol and interface that supports the information exchange Purchase hardware and software to make this happen.
Appendix Binary Number based system where only two characters exist, 0 and 1. Counting is 0, 1, 10, 11... 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. 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”.
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. 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.
Formerly referred to as RS(Recommended Standard). (See EIA-232, EIA-422, EIA-423 and EIA-485) This data is programmed once and cannot easily be changed as software can. Full See Full Duplex. Electronic Industries Association (EIA) An association in the US that establishes standards for electronics and data communications 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.
Mark Represents the transmission of data bit logic 1 (see logic level). Usually this is the most negative voltage value in serial communications. 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. Master The device on the bus that controls all communications. Only the master can initiate conversation.
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. 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.
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.
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 Comm4 Diagnostic Software 21 Comm5vb Diagnostic Software 21 Computer Languages 8 Controller Comparison Summery 22 Convention 4 CRC 21 D Disclaimer of Warranty 28 E Elements of Machine to Machine Comm.
How to Reach Us Contact Your Authorized Watlow Distributor: 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. • 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.
