Watlow 988 series User manual

$5.00
Made in the U.S.A.
Data Communications with the Watlow
Series 988 Family of Controllers
User's Manual
Includes:
981-984 Ramping
986-989 Temperature or Process
996-999 Dual Channel
Watlow Controls
1241 Bundy Blvd., P.O. Box 5580, Winona, Minnesota 55987-5580; Phone: [phone];
Fax: [phone]
W98F-XUMN Rev A03
Supersedes: W98F-XUMN Rev A02
June 1997 Printed on Recycled Paper, 10% Post-consumer Waste.
User Level Targeted:
• New User............................. Go to page 1.1
• Experienced User ................Go to page 2.1
• Expert User .........Go to page 5.1, 6.1 or 7.1
Installer:
• Wiring and installation.........Go to page 2.1
• Setup...................................Go to page 3.1
TL
W
W
A
PROCESS
1A 2A 1B 2B
CH A
CH B
DISPLAY
SERIES 998
MODE
AUTO
MAN
AUTO
MAN
TL
W
W
A
PROCESS
L1 L2 L3 L4
DEV
% OUT
DISPLAY
SERIES 982
MODE
HOLD
RUN
TL
W
W
A
PROCESS
L1 L2 L3 L4
DEV
% OUT
DISPLAY
SERIES 988
MODE

How to Use this Manual
We have designed this user’s manual to be a helpful guide to your new Watlow
controller. The headlines in the upper right and left corners indicate which tasks are
explained on that page. If you are a new user, we suggest that your read the first
four chapters of this manual.
Notes, Cautions and Warnings
We use notes, cautions and warnings throughout this book to draw your attention
to important operational and safety information.
A bold text “NOTE” marks a short message in the margin to alert you to an impor-
tant detail.
A a bold text “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 bold text “WARNING” safety alert appears with 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 çsymbol (an exclamation point in a triangle) precedes a general CAUTION
or WARNING statement.
The Ósymbol (a lightning bolt in a triangle) precedes an electric shock hazard
CAUTION or WARNING safety statement.
Technical Assistance
If you encounter a problem with your Watlow controller, review all of your configu-
ration information for each step of the setup, to verify that your selections are
consistent with your applications.
If the problem persists after checking all the steps, call for technical assistance:
Watlow Controls, [phone], between 7:00 a.m. and 5:00 p.m. Central
Standard Time. Ask for an applications engineer.
When you call, have the following information ready:
• the controller’s model number (the 12-digit number is printed on the top of the
stickers on each side of the controller case and on the right hand or top circuit
board);
• this user’s manual;
• all configuration information;
• the Diagnostics Menu readings.
Comments and Suggestions
We welcome your comments and opinions about this user’s manual and the Series
988 Family of controllers. Send them to the Technical Editor, Watlow Controls,
1241 Bundy Boulevard, P.O. Box 5580, Winona, MN 55987-5580. Or call (507)
454-5300 or fax them to [phone].
About This Manual
The Data Communications User’s Manual for the Series 988 Family is copyrighted
by Watlow Controls, Inc., © 1997, with all rights reserved. (1027)

Table of Contents Data Communications with the Watlow Series 988 Family of Controllers III
Table of Contents
Data Communications with the Watlow Series 988 Family of Controllers
Chapter 1
Introduction to Data Communications
1.1 Machine-to-Machine Communication
1.1 Protocol
1.1 A Protocol Example
1.3 RS-232, EIA-485 and RS-422 Interfaces
1.4 ASCII
1.4 Parity Bit
1.5 Start and Stop Bits
1.5 Baud Rate
1.5 Computer Languages
1.5 Syntax
1.6 ASCII Control Character Definitions
1.6 Data Communications Conversation
Chapter 2
Hardware and Wiring
2.1 Serial Hardware Interfaces
2.1 Your Computer’s Serial Interface
2.1 Communications Wiring
2.2 RS-232 Interface Wiring
2.3 EIA-485 Interface Wiring
2.4 RS-422 Interface Wiring
Chapter 3
Communications Setup
3.1 Connecting the Controller and Computer
3.1 Software Protocols and Device Addresses
3.2 Communications Software
3.2 Setup at the Controller's Front Panel
Chapter 4
Sending Commands
4.1 General Message Syntax
4.1 Message Syntax
4.1 Data Rules
4.1 Command List
4.2 Example Format
4.2 XON/XOFF Protocol for RS-232
4.2 How to Communicate Using XON/XOFF
4.3 How to Communicate Using ANSI X3.28
4.4 Device Addresses
4.5 ANSI X3.28 Protocol Example
4.6 Modbus RTU
4.10 Cyclical Redundancy Checksum (CRC)
Algorithm
Chapter 5
Command Summary of the Series 981-984
5.1 Complete Parameter Download Sequence
5.2 Run/Hold Mode and Prompt Accessibility
5.3 Ramping Controller Prompt Table
5.12 Ramping Controller MTR Command
5.13 Ramping Controller STP Command
5.14 Ramping Controller Commands Table
5.16 Modbus RTU Address Table
Chapter 6
Command Summary of the Series 986-989
6.1 Complete Parameter Download Sequence
6.2 Temperature/process Controller Prompt Table
6.13 Modbus RTU Address Table
Chapter 7
Command Summary of the Series 996-999
7.1 Complete Parameter Download Sequence
7.2 Dual Channel Controller Prompt Table
7.12 Modbus RTU Address Table
Appendix
A.1 Handling Communications Error Codes
A.1 User Responsibility
A.2 ASCII Characters
A.3 Index

Table of ContentsData Communications with the Watlow Series 988 Family of Controllers
IV
Table of Contents
NOTES

Introduction to Data Communications, Chapter 1 Data Communications with the Watlow Series 988 Family 1.1
Chapter 1 Introduction to Data Communications
NOTE:
This manual applies
only to controllers
with the data
communications
option (9___-____-
_R__ or 9___-____-
_S__ or 9___-____-
_U__). Please use it
in conjunction with
the user's manuals.
Machine-to-Machine Communication
Humans use basic components to exchange messages. Computers and controllers
also use certain elements in order to communicate: a character set; a common
data link, or interface; and a protocol, to prevent confusion and errors.
Serial communication is the exchange of data one bit at a time 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 typically simpler than parallel, it generally costs less.
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).
Bit is simply the contraction of "binary digit," either a "1" or a "0." A byte is a string
of seven or eight bits, which a computer treats as a single "character." The ASCII
(pronounced "asky") character set uses a unique, seven-bit byte to represent each
letter, digit and punctuation mark.
Protocol
Now we need a few rules to "talk" by. Protocol determines who gets to talk when. A
protocol is a set of standards for formatting and timing information exchange
between electronic systems.
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 different data
communications protocols, just as there are different human cultural protocols that
vary according to the situation.
A Protocol Example
Let's assume that we have a computer and controllers linked together. They all use
ASCII and are connected via a common interface. In process control applications,
one device often has greater function and memory capability than the devices it is
communicating with. This "master" device always initiates exchanges between it
and the connected "remote" devices.
Here's what happens: Imagine "PC-1," the master computer, sitting at the end of a
long hallway with nine doors in it. Each door has a remote device behind it. PC-1
has a telephone line to all the devices. The remote devices are busy controlling
heaters to specific set points. PC-1 monitors and changes the instructions that
each remote device uses to control its heaters.

1.2 Introduction to Data Communications, Chapter 1 Data Communications with the Watlow Series 988 Family
By your request PC-1 wants to talk with device "D-2" to change a set point. PC-1
must first identify D-2 on the line and inquire whether D-2 has time to talk. This
electronic knocking on D-2's door is the "connection."
One of three scenarios may occur when PC-1 calls:
1) D-2 answers saying, "This is D-2, go ahead," and PC-1 begins to talk.
2) D-2 answers and says, "I'm too busy to talk now. Wait until I tell you I'm
finished."
3) D-2 does not answer, which indicates a possible system malfunction.
Let's take the best-case scenario. Here is a simple version of what happens: D-2
answers and hears PC-1 say, "Hello, D-2. Do you have time to talk?"
D-2 acknowledges PC-1 with a "D-2 here, go ahead."
PC-1 then sends an ASCII-encoded message instructing D-2 to change a set point
to 1,000°F. (message)
When PC-1 is finished with its message, it says in effect, "That's all, your turn."
D-2 replies, "OK," and carries out the instruction. D-2 then takes the protocol lead,
and tells PC-1, "The new set point is 1,000°F." (message)
PC-1 says, "OK."
D-2 says, "That's all, your turn."
PC-1 then takes the protocol lead and says, "Thank you, that's all."
D-2 hangs up. (disconnect)
That's basically how the connect, message and disconnect protocols work in
Watlow data communications.
The hallway in this example is really a communications bus — a common connec-
tion among a number of separate devices. A communications system with multiple
devices on a common bus is called a multidrop system.
The exacting connect-message-disconnect procedure assures that you are talking
to the correct device.
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 operator or 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.
Interfaces

Introduction to Data Communications, Chapter 1 Data Communications with the Watlow Series 988 Family 1.3
Interfaces
0V
1 bit
0 bit
-12V
+12V
Bit signals on an RS-232 interface.
+5V
0V
-5V
1 bit
1 bit
+5V
0V
-5V
0 bit
Bit signals on an RS-422 interface.
Bit signals on an EIA-485 interface.
Figure 1.3 - Interface
bit signals.
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. Up to 32 remote devices
can be connected to a master on a multi-drop network up to 4,000 feet long.
The RS-422 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 network
up to 4,000 feet long. RS-422 uses the difference in voltage between the two wires
to indicate a 1 or a 0 bit. A 1 is a difference of +5 volts, while a 0 is a difference of
-5 volts.
Of these three interfaces, EIA-485 has the lowest impedance, a multiple-device
capability, greatest noise immunity and the longest distance capability — up to
4,000 feet of total network cable length.
RS-232, EIA-485 and RS-422 Interfaces
The three interfaces we're concerned with on this controller are RS-232, EIA-485
and RS-422.
An RS-232 interface uses three wires: a single transmit wire; a single receive wire;
and a common line. Only two devices can use an RS-232 interface. A -12 volt
signal indicates a 1 and a +12 volt signal indicates a 0. The RS-232 signal is
referenced to the common line rather than to a separate wire, as in EIA-485 and
RS-422. An RS-232 cable is limited to 50 feet, due to noise susceptibility.
0 bit

1.4 Introduction to Data Communications, Chapter 1 Data Communications with the Watlow Series 988 Family
Maximum Maximum Cable
Net Length Controllers Type
RS-232 50 feet 1 3-wire
EIA-485 4,000 feet 32 3-wire
RS-422 4,000 feet 10 5-wire
ASCII
The ASCII code defines 128 separate 7-bit characters — one for each letter, digit
and punctuation mark. ASCII also includes control characters similar to those we
find on computer keys, like "backspace," "shift" and "return." It also has ten com-
munications 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, called hexa-
decimal or "hex" for short. The first ten digits of this system are represented by the
numbers 0 through 9, and the final six digits are represented by the letters A
through F. The 128 ASCII character code with the decimal and hexadecimal
equivalents is listed in the Appendix.
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. Here's how: We are declaring that the number of 1s
in the 8-bit character frame will be either always odd or always even. To do that,
about half the time we'll have to add another 1 to get an odd or an even number of
ones. The other half of the time we'll need to add a 0 so we don't change the total
number of 1s.
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 case 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.
If we were transmitting the lower case "w" (binary 1110111), the parity bit would be
a 1 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 1 to a 0 in the character frame, the receiver would detect that
Table 1.4 - Compar-
ing Interfaces.
NOTE:
The Modbus feature
on the Series 988
controllers allows up
to 247 controllers to
share one EIA-485
network, by using
network bridges.
See Chapter 6 for
more information on
Modbus.
Figure 1.4 - ASCII
upper case "W"
(1010111).
7-bit character
odd parity bit
bit position: 12345678
1
0
ASCII

Introduction to Data Communications, Chapter 1 Data Communications with the Watlow Series 988 Family 1.5
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
bits.
Even 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 one is complete. The start bit is always a 0. The stop bit is always a 1.
We've added the start and stop bits to the transmitted "W" example.
The human speaking 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.
7-bit character
12345678
1
0
idle line
start bit
stop bit
odd parity bit
Figure 1.5 - ASCII
upper case "W" with
start and stop bits.
Baud Rate
The baud rate refers to the speed of data transmission. When a change in signal
represents one data bit, baud rate is equal to bits per second (bps). Our rates on
the 988 Family of controllers are 300, 600, 1200, 2400, 4800 and 9600 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. Program-
mers use languages to enable computers to do real work. We're providing a pilot
program written in Quick BASIC to demonstrate data communications with Watlow
controllers. You can download it ("comms4.zip" and "comms4tm.zip") from the
Watlow BBS, [phone].
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.
ASCII

1.6 Introduction to Data Communications, Chapter 1 Data Communications with the Watlow Series 988 Family
Syntax
For example, the Series 986-989 parameter for set point information is SP1. The
controller's panel will normally display SP1 and set point information whenever you
physically press the DISPLAY key to reach SP1 in the parameter sequence. For a
computer linked to a controller, "SP1" is part of the syntax for data communica-
tions.
If you type just "SP1" on the computer keyboard, the controller won't respond to
your computer with the current set point 1 data. The syntax requires spaces and
"fields" of specific size to be complete.
Plus, we need to add the protocol. It's like putting a message in an envelope and
addressing it. The entire syntax of the SP1 command includes the message
protocol's STX (Start of Text) control character, SP1, space, up to four decimal
places of set-point data, and a protocol ETX (End of Text) control character.
The whole phrase would look like this:
<STX> SP1 0500 <ETX>
ASCII Control Character Definitions
ENQ Enquiry (inquiry): Request for a data link.
ACK Acknowledge: Affirmative response from the receiver.
NAK Negative Acknowledge: Negative response from the receiver.
STX Start of Text: Precedes any message from the sender.
ETX End of Text: Follows any message from the sender.
EOT End of Transmission: Tells the other device that it is its turn to send a mes-
sage.
DLE Data Link Escape: Disconnect signal from the master to devices on the
network.
A Data Communications Conversation
Now that you have a general grasp of the basic ideas and terms behind data
communications, we'll take the example further to see how an actual conversation
would take place.
The example on the next page follows the exchange between a computer (master)
and a controller (remote) as the computer sends a set point data command to the
controller.
That's really all there is to it. Remember — only the "master" may initiate ex-
changes and every message requires a response.