Watlow 988 User Manual

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

W

A

TL

W

PROCESS

[`982]

L1 L2 L3 L4

DEV

% OUT

SERIES 982

DISPLAY

HOLD

RUN

MODE

SERIES 988

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

A

TL

W

PROCESS

[`988]

L1 L2 L3 L4

DEV

% OUT

DISPLAY

AUTO

MAN

MODE

W

W

PROCESS

W

A

TL

[`998]

1A 2A 1B 2B

CH A
CH B

SERIES 998

DISPLAY

AUTO

MAN

MODE

Watlow Controls

1241 Bundy Blvd., P.O. Box 5580, Winona, Minnesota 55987-5580; Phone: [phone];

0600-0009-0004 Rev B

Supersedes: W98F-XUMN Rev A03
February 1998

Fax: [phone]

97

TOTAL

CUSTOMER

SATISFACTION

ISO 9001

Registered Company

Winona, Minnesota USA

$15.00

Made in the U.S.A.

Printed on Recycled Paper, 10% Post-consumer Waste.

About This Manual

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 impor­tant detail.

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 ç symbol (an exclamation point in a triangle) precedes a general CAUTION
or WARNING statement.

The Ó symbol (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 configu­ration 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) 454­5300 or fax them to [phone].

Warranty and Returns

For information about the warranty covering the Series 988 family of controllers
see the Appendix.
The Data Communications User’s Manual for the Series 988 family is copyrighted
by Watlow Controls, Inc., © 1997, with all rights reserved. (1385)

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 EIA-232, EIA-485 and EIA-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

2.2 Communications Wiring

2.2 EIA-232 Interface Wiring

2.3 EIA-485 Interface Wiring

2.4 EIA-422 Interface Wiring

Chapter 3
Communications Setup

3.1 Connecting the Controller and Computer

3.1 Software Protocols and Device Addresses

3.1 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 EIA-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

5.16 982 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

6.13 988 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

7.12 998 Modbus RTU Address Table

Appendix

A.1 Handling Communications Error Codes
A.1 User Responsibility
A.2 ASCII Characters
A.3 Index

Table of Contents Data Communications with the Watlow Series 988 Family of Controllers

III

Table of Contents

NOTES

IV

Table of ContentsData Communications with the Watlow Series 988 Family of Controllers

Chapter 1 Introduction to Data Communications

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

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.

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.

Interfaces

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.

Introduction to Data Communications, Chapter 1 Data Communications with the Watlow Series 988 Family

1.1

Interfaces

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 exact 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.

1.2

Data Communications with the Watlow Series 988 Family

Introduction to Data Communications, Chapter 1

Interfaces

EIA-232, EIA-485 and EIA-422 Interfaces

The three interfaces we're concerned with on this controller are EIA-232, EIA-485
and EIA-422.

An EIA-232 interface uses three wires: a single transmit wire; a single receive wire;
and a common line. Only two devices can use an EIA-232 interface. A -12 volt
signal indicates a 1 and a +12 volt signal indicates a 0. The EIA-232 signal is
referenced to the common line rather than to a separate wire, as in EIA-485 and
EIA-422. An EIA-232 cable is limited to 50 feet, due to noise susceptibility.

Figure 1.3 - Interface
bit signals.

0 bit

1 bit

Bit signals on an EIA-232 interface.

+12V

0 bit

1 bit

0V

Bit signals on an EIA-485 interface.

-12V

0 bit

1 bit

Bit signals on an EIA-422 interface.

+5V

-5V

+5V

-5V

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.

0V

0V

The EIA-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. EIA-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.

Introduction to Data Communications, Chapter 1 Data Communications with the Watlow Series 988 Family

1.3

ASCII

Table 1.4 - Compar­ing Interfaces.

Maximum Maximum Cable
Net Length Controllers Type

EIA-232 50 feet 1 3-wire
EIA-485 4,000 feet 32 3-wire
EIA-422 4,000 feet 10 5-wire

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.

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 com­munications control characters for "identification," "enquiry" (inquiry), "start of text,"
"end of text," "end of transmission," "acknowledge," "negative acknowledge" and
"escape."

The ASCII code is sometimes written in a base-16 number system, called hexa­decimal 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.

Figure 1.4 - ASCII
upper case "W"
(1010111).

1.4

Data Communications with the Watlow Series 988 Family

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

7-bit character

+V

-V

bit position: 12345678

0
1

odd parity bit

Introduction to Data Communications, Chapter 1

ASCII

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.

Figure 1.5 - ASCII
upper case "W" with
start and stop bits.

-V

+V

idle line

1
0

start bit

7-bit character

12345678

stop bit

odd parity bit

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. Program­mers 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 the MS-DOS™ version files ("comms4.zip" and
"comms4tm.zip" and com5set.exe) 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.

Introduction to Data Communications, Chapter 1 Data Communications with the Watlow Series 988 Family

1.5

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 communica­tions.

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.

1.6

That's really all there is to it. Remember — only the "master" may initiate ex­changes and every message requires a response.

Data Communications with the Watlow Series 988 Family

Introduction to Data Communications, Chapter 1

An Example of a Data Communication Conversation

Syntax

The computer (the master) initiates an
exchange with controller #2 (the remote).

The computer tells the controller to
change its set point.

The computer queries the controller for
the new set point.

computer

2 <ENQ> (#2, are you there?)

controller

2 <ACK> (I'm #2, I'm here.)

computer

<STX> = <space> SP1 <space> 500 <return> <ETX>

("Here comes a message."
"Make SP1 = 500°."
"I'm done with the message.")

controller

<ACK> ("I understand.")

computer

<STX> ? <space> SP1 <return> <ETX>

("Here comes a message."
"What is SP1 value?"
"I'm done with the message.")

controller

<ACK> ("I understand [the question].")

The controller confirms that the new set
point.

The computer ends the session.

computer

<EOT> ("That's all, go ahead.")

controller

<STX> 500 <ETX>

( "Here comes the answer."
"The value is 500°."
"I'm done with the answer.")

computer

<ACK> ("I understand [the answer].")

controller

<EOT> ("That's all, go ahead.")

computer

<DLE> <EOT> ("Disconnect, please. That's all."

[master waits])

Introduction to Data Communications, Chapter 1 Data Communications with the Watlow Series 988 Family

1.7

Introduction

Notes

1.8

Data Communications with the Watlow Series 988 Family

Introduction to Data Communications, Chapter 1

Chapter 2 Hardware and Wiring

Serial Hardware Interfaces

The Series 981-984, 986-989 and 996-999 controllers are factory-configured to
function in a broad variety of applications. The specifics of each controller's con­figuration is encoded in its model number. Depending on your unit's model number,
you have one of three hardware interfaces:

1) EIA-232 (9___-____-_R__) provides one-on-one communication with a maxi-

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.

mum network length of 50 feet connecting one controller to one computer.

2) EIA-485 (9___-____-_S__) provides a "multidrop" or multiple-device network
with up to 32 addresses with a 4,000-foot network length limit. EIA-422 pro­vides a multidrop network for up to ten devices with a 4,000-foot network
length limit. To select the multidrop interface, enter the Setup Menu

[`SEt]. Use the up-arrow or down-arrow key to advance to the Communica-
tions Menu [COM]. Press the MODE key until the interface prompt [IntF]

appears. Select either 485 or 422.

3) EIA-232/EIA-485 (9___-____-_U__) If your controller is supplied with a "U"
board, you can select via the comms menu either EIA-232 or EIA-485 opera­tion. The [IntF] parameter is defaulted to EIA-232. To select the multidrop
interface, enter the Setup Menu [`SEt]. Use the up-arrow or down-arrow key
to advance to the Communications Menu [COM]. Press the MODE key until
the interface prompt [IntF] appears. (Controllers equipped with the EIA-
232 interface do not require an interface selection.)

Hardware

Your Computer's Serial Interface

You can connect a data communication-equipped Series 981-984, 986-989 or 996­999 to any computer with an EIA-422, EIA-232 or EIA-485 serial interface. A
personal computer with an EIA-232 serial output card, for instance, can talk to a
single EIA-232 equipped controller.

For a multiple-controller network with one personal computer, you'll need a con­verter to act as a bus, or multiple connection point.

For data communications serial interface converters for EIA-232 (RS-232), we
recommend either of these two suppliers:

• DATAFORTH Corp. (formerly supplied by Burr-Brown):

3331 E. Hemisphere Loop, Tuscon, AZ 85706
Tel: [phone], or [phone] or Fax: [phone]
For EIA-422 (RS-422), part number: LDM 422
with a power supply and the correct 25 pin connector for your computer.
For EIA-485 (RS-485), part number: LDM 485
with a power supply and the correct 25 pin connector for your computer.

• B & B Electronics Manufacturing Company

707 Dayton Road, PO Box 1040, Ottawa, IL 61350
Tel: [phone] or Fax: [phone] or Web: http://www.bb-elec.com
For EIA-422/ EIA-485 (RS-422/ RS-485), part number: 485OIC
with a power supply and the correct 25 pin connector for your computer.

Hardware and Wiring, Chapter 2

Data Communications with the Watlow Series 988 Family

2.1

Wiring

NOTE:
The Electronic
Industry Association
(EIA) RS-232
standard recom­mends a maximum
50-foot total point­to-point distance.

Communications Wiring

The rest of the chapter explains how to connect your controller to a computer.
Consult the instruction manual for your computer's serial port or serial card for
detailed serial port pin information. Industrial environments often contain a lot of
electrical noise. Take care to isolate your control system.

EIA-232 Interface Wiring

The EIA/-232 communications uses a three-wire, full-duplex system. There is a
separate line for transmitting data, a line for receiving data and a common line
between the computer and the controller. With EIA-232 you can have only one
controller connected to a single computer.

This diagram is a typical wiring example. The connections on the host computer
may vary, depending on the model. Refer to your computer or serial card user's
manual for specific information.

DB-9 Pinouts

1 DCD
2 receive
3 transmit
4 DTR
5 common
6 DSR
7 RTS
8 CTS

• • • • •
1 2 3 4 5

Transmit 5
Receive 6
Common 7

Figure 2.2 ­EIA-232 Interface
Wiring Diagrams.

6 7 8 9

• • • •

DB-9 female viewed from wire side
(typical connections with jumpers)

DB-25 Pinouts

2 transmit
3 receive
4 RTS
5 CTS
6 DSR
7 common
8 DCD
20 DTR

• • • • • • • • • • • • •
1 2 3 4 5 6 7 8 9 10 11 12 13

14 15 16 17 18 19 20 21 22 23 24 25

• • • • • • • • • • • •

DB-25 female viewed from wire side
(typical connections with jumpers)

Single Controller

Transmit 5
Receive 6
Common 7

Single Controller

2.2

Data Communications with the Watlow Series 988 Family

Hardware and Wiring, Chapter 2

NOTE:
The Electronic
Industry Association
EIA-485 standard
recommends a
maximum total
network distance of
4,000 feet.

Wiring

EIA-485 Interface Wiring

The EIA-485 communications uses a three-wire, half-duplex system. There are two
lines for transmitting and receiving and a common line. Only one device, the
computer or a controller, can be speaking at a time. The controller requires at
least a 7-millisecond delay between transmission and receipt of data. With
EIA-485 you can have from one to thirty-two controllers connected to a computer.

This diagram is a typical wiring example for units shipped after 1993 (see ç
Caution on this page). The connections on the host computer may vary, depend­ing on the model. Refer to your computer user's manual for specific information.

As many as 32 units can be
connected to an EIA-485 network.

T-/R- 3
T+/R+ 4

Com 7

Controller

ç

CAUTION:
For older Series 986­989 controllers with
a "date code" of
4693 or earlier,
terminal 3 is T-/R- (A)
and 4 is T+/R+ (B).
(See Diagnostics
Menu in the User's
Manual.)

B
A

Gnd

Converter Box or Card

T+/R+
T-/R-

Com

T+/R+ 3
T-/R- 4

Com 7

Controller #1

T+/R+ 3
T-/R- 4

Com 7

Controller #2

Figure 2.3 ­EIA-485 Interface
Wiring Diagrams.

Hardware and Wiring, Chapter 2

Converter box
or card
terminals with
termination,
pull-up and
pull-down
resistors.

+5V

Gnd

B

A

1KΩ

T+/R+

120Ω

T-/R-

1KΩ

Com

If the system does not work properly it
may need termination resistors at each
end of the network. A typical installa­tion would require a 120-ohm resistor
across the transmit/receive terminals (3
and 4) of the last controller in the
network and the converter box or serial
card. Pull-up and pull-down resistors
may be needed to maintain the correct
voltage during the idle state.

Data Communications with the Watlow Series 988 Family

2.3

Wiring

NOTE:
The Electronic
Industry Association
(EIA) RS-422
standard recom­mends a maximum
network distance of
4,000 feet.

EIA-422 Interface Wiring

The EIA-422 communications uses a five-wire, full-duplex system. There are two
separate lines for transmitting, two lines for receiving and a common line between
the computer and the controller. With EIA-422 you can connect from one to ten
controllers to a single computer.

This diagram is a typical wiring example for units shipped after 1993 (see ç
Caution on this page). The connections to the converter box or computer may
vary, depending on the model. Refer to the documentation for specific information.

B'
A'

Gnd

R+
R­T+

B

T-

A

Com

T+ 3
T- 4
R+ 5
R- 6
Com 7

Figure 2.4 ­EIA-422 Interface

Wiring Diagrams.

ç

CAUTION:
For older Series
986-989 control­lers with a "date
code" of 4693 or
earlier, terminal
3 is T-, 4 is T+, 5
is R- and 6 is
R+. (See Diag­nostics Menu in
the User's
Manual.)

T- 3
T+ 4
R- 5
R+ 6
Com 7

Converter Box or Card

As many as 10 units
can be connected to
an EIA-422 network.

Controller

Controller #1

T+ 3
T- 4
R+ 5
R- 6
Com 7

Controller #2

Converter
box with
termination
pull-up and
pull-down
resistors.

RD

TD

+5V

B
A
B
A

Gnd

1KΩ

240Ω

1KΩ

If the system does not work properly it may need
termination resistors across the receive A and B termi­nals at the converter. A typical value would be 240Ω.
Pull-up and pull-down resistors may be needed to
maintain the correct voltage during the idle state.

2.4

Data Communications with the Watlow Series 988 Family

Hardware and Wiring, Chapter 2

Chapter 3 Communications Setup

Connecting the Controller and the Computer

Remove power from both the controller and your computer before connecting them
together. Assemble a cable and the appropriate wiring at your computer. Refer to
the wiring in Chapter 2. As soon as you connect the data communications lines,
you may apply power to your system.

Software Protocols and Device Addresses

There are three communications protocols you may use. Depending on the type of
network you need, you must use the correct combination of interface and protocol.
Modbus works with all three interfaces.

To run a network with multiple devices Watlow uses the ANSI X3.28 Protocol
(based on ANSI X3.28 - 1976 Subcategories 2.2, and A.3) with the EIA-422 and
EIA-485 interface. ANSI X3.28 Protocol provides a response to every message. It
will also work with the EIA-232 interface, but you are limited to one controller and a
host computer.

Setup

To run a two-device network with an EIA-232 interface, you can also use XON/
XOFF Protocol, a simpler protocol. XON/XOFF will also work with the EIA-422 and
EIA-485 interface, but the network is limited to two devices — one computer
and one controller. XON/XOFF Protocol does not require a device to respond to
messages it receives.

To select the protocol, go to the Setup Menu [`SEt]; use the up-arrow or down­arrow key to advance to the Communications Menu [COM]. Press the MODE key
until the protocol prompt [Prot] appears. Select either [FULL], for ANSI X3.28 2.2

- A.3, [``On] for XON/XOFF, or [Mod], for Modbus RTU.

If you are using ANSI X3.28 Protocol, choose an address number for each control­ler using the address prompt [Addr], which follows the protocol prompt [Prot].
This prompt will only appear if [Prot] is set to [FULL] or [Mod].

Communications Software

Watlow offers a Windows based configuration and monitoring software package for
the 988/989 controllers. We also offer a simple MS-DOS™ communications
demonstration program for the Series 981-984, 986-989, and 996-999. Ask your
Watlow field sales representative for a copy of the "Comm 4" program, or you can
download the files ("comms4.zip" and "comms4tm.zip" and com5set.exe) from the
Watlow BBS, [phone].

Communications Setup, Chapter 3

Data Communications with the Watlow Series 988 Family

3.1

Setup

(

Figure 3.2 ­The Communications
Menu.

W

A

TL

W

PROCESS

L1 L2 L3 L4

DEV

DISPLAY

% OUT

HOLD

MODE

SERIES 988

RUN

Communications)

Baud rate
Data bits and parity

Protocol type

Address
Interface type

[COM]

(COM)

bAUd

[bAUd]

dAtA

[dAtA]

Prot

[Prot]

Addr

[Addr]

intF

[IntF]

( )
( )

( )
( )

( )

Setup at the Controller's Front Panel

• Press the < and > keys simultaneously for three seconds.

• The [SEt] prompt appears in the lower display.

• Press the < or > key until the [COM] prompt appears.

• Press the µ key to advance through the Communications Menu.

• Press the < or > key to select communications values from the table below.

NOTE:
Selecting [Mod]
automatically sets
[dAtA] to [``8n].

Table 3.2 ­Communications
Menu Prompts and
Descriptions.

• Document the setup parameters for each device on your network and label each
device.

• Press the ∂ key to exit.

Prompt Appears if… Range Factory

default

[bAUd] comms unit (Baud rate) [`300], [`600],

[1200], [2400], [4800], [9600] [9600]

[dAtA] comms unit [``7o] = 7 data bits, odd parity [``7o]

[``7E] = 7 data bits, even parity (see note)
[``8n] = 8 data bits, no parity

(Start bit = 1) (Fixed)
(Stop bit = 1) (Fixed)

[Prot] comms unit [FULL] = ANSI X3.28 2.2 - A.3 [FULL]

[``On] = XON / XOFF
[Mod] = Modbus

[Addr] [Prot] = [FULL] 0 to 31 (ASCII) if [IntF] = [`485] [```0]

or 0 to 9 (ASCII) if [IntF] = [`422] [```0]

[Prot] = [Mod] 1 to 247 if [IntF] = [Mod] [```1]

[IntF] "S" hardware [`485] = EIA-485 Interface type [`485]

[`422] = EIA-422 Interface type

[IntF] "U" hardware [`232] = EIA-232 Interface type [`232]

[`485] = EIA-485 Interface type

3.2

Data Communications with the Watlow Series 988 Family

Communications Setup, Chapter 3

Chapter 4 Sending Commands

General Message Syntax

As soon as you link the devices, you can talk to the controllers using ASCII charac­ters. They will respond to any Setup or Operation menu prompt, plus some others.
The controller will respond to either upper or lower case ASCII characters from
your computer.

Both protocol/interface combinations will respond to the general syntax if the
commands or queries are correctly transmitted. However, the ANSI X3.28 Protocol
requires beginning and ending characters, and the XON/XOFF protocol requires
ending characters.

Message Syntax

Messages from your computer to a controller must take this general form.

Command <space> data.1 <space> data.2 <space> data.3... data.N

"Command" is a character string. The brackets "<" and ">" enclose a non-literal

ç

CAUTION:
Avoid writing <=>
continuously, such
as ramping set
points or repetitive
loops, to the
controller's
EEPROM memory.
Continuous writes
may result in
premature control
failure, system
downtime and
damage to pro­cesses and equip­ment.

description. The space character, <space> or <sp>, is simply a delimiter, an ASCII
space character (hex 20). "Data fields" are prompts and values specific to the
command. The number of data fields depends on the particular command. The first
argument or parameter is abbreviated, "data.1," the next is "data.2," and so on.

In the syntax explanations that follow, we show you the specific arguments for each
command. It will speed the process if you remember this general syntax.

Data Rules

Data fields are prompts and values specific to particular commands. Specific data
for each command for each type of controller is listed after this chapter. These
rules govern their use:

• Data will include the characters 0 through 9; a decimal point if needed; or a

positive or negative sign.

• Data can include up to seven characters. A "+" or "-" sign, if used, must be first.

• Data can use leading zeros, up to the seven-character limit.

• The data.1 portion of message can be up to four total characters.

Sending Commands, Chapter 4

Command List

These commands, represented by their respective ASCII characters, will enable
you to program the controller from your computer. More detailed descriptions of the
commands are in Chapters 5, 6 and 7.

? Returns the value of a specific prompt from the controller.
= Sets a specific prompt in the controller to a specific value.

Data Communications with the Watlow Series 988 Family

4.1

XON/XOFF

Example Format

This manual presents command examples in a consistent format. Information
bracketed by < > indicates a description, rather than literal characters. We show
each ASCII character that you must transmit to the controller, including space
between the characters. (A <space>, or <sp>, is itself an ASCII character, hex 20).

For instance, in the example below, you want to set the Alarm 2 Low [A2LO]
prompt to 500°. Notice how the syntax uses the "=" command.

= <space> A2LO <space> 500 <carriage return>

To send this message, key the ASCII characters into your computer, or write them
into your program. Remember, your computer will send the ASCII character string
for the number, not an actual number. The hex string for the line looks like this:
3D2041324C4F203530300D.

Notice that we have not mentioned protocol here, or any characters added to this
syntax by a protocol. With XON/XOFF, the message above can be transmitted with
only an additional carriage return <cr> (hex 0D) character at the end. However, the
ANSI X3.28 Protocol requires an envelope of Start of Text <STX> (hex 02) and
End of Text <ETX> (hex 03) characters around the information you see above. You
will learn how to do that in the following pages.

XON/XOFF Protocol for EIA-232

XON/XOFF (flow control) protocol allows a communicating device (either a

controller or the host) to suspend transmission of all messages from the other
device, and then to continue transmission when it's again ready.

The device that needs to suspend transmission sends the XOFF character
(hex 13) to stop the other device's transmission, and XON (hex 11) to restart it.
Any character will restart the transmission, but to avoid confusion use only the
XON character.

Messages transmit according to the syntax described in the XON/XOFF formats
that follow for each command.

The XON/XOFF protocol requires a carriage return <cr> character
(hex 0D) at the end of every message.

How To Communicate Using XON/XOFF

XON/XOFF protocol is used when one master is networked with only one control­ler. Your personal computer must generate the master’s messages.

4.2

Data Communications with the Watlow Series 988 Family Sending Commands, Chapter 4

"=" Command Example

ANSI X3.28

ç

CAUTION:
Avoid writing <=>
continuously, such
as ramping set
points or repetitive
loops, to the
controller's
EEPROM memory.
Continuous writes
may result in
premature control
failure, system
downtime and
damage to pro­cesses and equip­ment.

Master:
Remote:

master must stay off line.)

Remote:

Note: The commands IN1, IN2 and CF may take up to two seconds to return this
character. Do not send another message until this character is received.)

“?” Command Example”

Master:
Remote:

off-line.)

Remote:

another message once the <cr> is received.)

message.)

For maximum communications speed:

• Do not use a typical delay to wait before looking for a response.

• Scan for returned characters until the correct response is received.

• Use a time out to end a session if a correct response is not received in three

= <sp> A2LO <sp> 500 <cr> (Set the A2LO prompt value to 500.)

<XOFF> (This will be returned once the device starts processing. The

<XON> (Processing is done. The master may send a new message.

? <sp> A2LO <cr> (Request the A2LO prompt value.)

<XOFF> (The remote is preparing the response. The master must stay

<XON> 500 <cr> (The value is returned and the master may send

or
<XON> (The message was not understood. The master may send a new

seconds.

How to Communicate Using ANSI X3.28

The ANSI X3.28 protocol provides high quality communications by requiring a
response to every message. With a multiple-device or "multidrop" network, this
protocol prevents confusion among the separate devices. Furthermore, if noise
occurs somewhere in the system, no prompt will change because noise cannot
comply with the protocol.

By placing messages inside a protocol envelope, the messages are protected. In
the following examples you'll see how this works.

ANSI X3.28 protocol rules:

• Every remote device must have a unique address.

• Only the master can initiate a communication session, by addressing a specific

remote device.

• Every message must be framed with an <STX> (start of transmission) character

and an <ETX> (end of transmission) character.

• The master must wait for the remote device to respond to every message within a

reasonable period. If no response occurs, retry the connection or pursue error
recovery.

Sending Commands, Chapter 4

Data Communications with the Watlow Series 988 Family

4.3

ANSI X3.28

Table 4.4 ­Address to ASCII
Conversion for ANSI
X3.28 Protocol.

Device Addresses

A Watlow EIA-422 multidrop network can handle up to 10 devices with this proto­col. EIA-485 can handle up to 32 devices. Set the address number of the controller
with the address prompt [Addr] under the Setup Menu [`SEt].

ASCII

Address Equivalent

00
11
22
33
44
55
66
77
88

99
10 A
11 B
12 C
13 D
14 E
15 F
16 G
17 H
18 I
19 J
20 K
21 L
22 M
23 N
24 O
25 P
26 Q
27 R
28 S
29 T
30 U
31 V

4.4

Data Communications with the Watlow Series 988 Family Sending Commands, Chapter 4

ANSI X3.28

ANSI X3.28 Protocol Example

This example demonstrates communication between a master device and a remote
device at address 4. Your personal computer must generate the master’s messages.

Establish Communications Link

Master:
Remote:

End Communications Link

Master:
Remote:

“=” Command Example

Master:
Remote:

Note: The commands IN1, IN2 and CF may take up to 2 seconds to return this character.
Do not send another message until this character is received.)

“?” Command Example

Master:
Remote:

not send the <EOT> until this character has been received.)

Master:
Remote:

send a response until the <ETX> has been received.)

4 <ENQ> (Attempt to link with device 4.)
4 <ACK> (The link is established.)

<DLE> <ENQ> (End data link.)

No response.

<STX> = <sp> A2LO <sp> 500 <ETX> (Set A2LO prompt value to 500.)
<ACK> (This will be returned once the unit has completed the value change.

<STX> ? <sp> A2LO <ETX> (Request the A2LO prompt value.)
<ACK> (This will be returned once the device has the response ready. Do

or

<NAK> (The command was not understood. Re-send corrected message.)
<EOT> (The host gives the device permission to respond.)

<STX> 500 <ETX> (The device sends back the requested value. Do not

Master:

Remote:

until this character has been received.)

For maximum communications speed:

• Do not use a typical delay to wait before looking for a response.

• Scan for returned characters until the correct response is received.

• Use a time out to end a session if a correct response is not received in three seconds.

• Protocols are not flexible. Outside of the <STX> <ETX> framing only the defined

• End the communications link and re-establish it with <DLE> and <ENQ> only when

Sending Commands, Chapter 4

<ACK> (The host received the message correctly.)
or

<NAK> (The host did not understand the response.Device will re-send it.)
<EOT> (The device returns control to the host. Do not send a new message

Try again later.
protocol characters are allowed. Some programming languages add <cr> to the end

of transmissions. This must be disabled.
changing to a new device at a different address. The master can communicate

repeatedly with a specific device once the initial data link is established.

Data Communications with the Watlow Series 988 Family

4.5

Modbus RTU

NOTE:
Modbus register
addresses are
listed in the
Controller Prompt
Table later in this
chapter and in the
Modbus RTU
Address Table at
the end of this
chapter.

Modbus Remote Terminal Unit (RTU)

Modbus RTU, available on the 988 family of controllers, expands the communica­tions ability of the controller by enabling a computer to read and write directly to
registers containing the controller’s parameters.

Because of the wide array of choices available for setting up the 988 family of
controllers, only a subset of the prompts contain parameters in a given situation. The
Series 982, 988 and 998 User’s Manuals explain the interrelations between prompts.
If you try to write to an inactive prompt the controller will return an illegal data ad­dress message (02). (See “Exception Responses,” pg. 4.9.)

If you already have a software application that uses Modbus, you can simply skip to
the Temperature/process Controller Prompt Table or the Modbus RTU Address
Table in this chapter for the address information your program will need. The rest of
this section on the Modbus provides information for writing a software application that
uses Modbus.

Writing a Modbus Application

You need to code messages in eight-bit bytes, with no parity bit. Negative parameter
values must be written in two's complement format. Parameters are stored in two­byte registers accessed with read and write commands to a relative address.
Messages are sent in packets that are delimited by a pause at least as long as the
time it takes to send 30 bits. To determine this time in seconds, divide 30 by your
baud rate.

Because changing some parameters automatically changes or defaults other param­eters, use the Complete Parameter Download Sequence table in this chapter to
order write commands.

Using a controller address of 0x00 for a write command broadcasts that command to
all the controllers in the network. This is a powerful feature if all the controllers on a
network use all or most of the same parameters. No response is given to broadcast
messages. Be sure to read each control to ensure it has received the command.

4.6

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.

Packet format: nn | nn | nnnn… | nnnn

∆∆∆∆ ∆∆

address
command
registers and/or data
CRC

Data Communications with the Watlow Series 988 Family Sending Commands, Chapter 4

NOTE:
Because the read
command can
only read 32
registers, the high
byte for the
number of regis­ters will always be

0.

Modbus RTU

Read Multiple Registers Command (0x03 or 0x04)

This command returns from 1 to 32 registers.
Packet sent to controller:| nn | 03 | nnnn | 00 nn | nn nn |

∆∆∆∆∆∆∆∆

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

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

∆∆∆∆∆∆∆∆∆

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

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).

Sending Commands, Chapter 4

Example (988 only): Read register 1 and 2 (Process 1 and 2 values) of controller at
address 5.
Sent: 05 03 00 01 00 02 94 4F
Received: 05 03 04 00 64 00 C8 FF BA
Message: 100 (0x0064) and 200 (0x00C8).

Write to a Single Register Command (0x06)

This command writes a parameter to a single register. The controller will echo back
the command. An attempt to write to a read-only parameter returns an illegal data
address 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 byte
register low byte
data high byte
data low byte
CRC low byte
CRC high byte

Data Communications with the Watlow Series 988 Family

4.7