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Chapter 4 Sending Commands
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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 pro-
cesses and equip-
ment.
Sending Commands, Chapter 4
General Message Syntax
As soon as you link the devices, you can talk to the controllers using ASCII charac-
ters. 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
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.
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
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