Red Lion PCU - Manual (Page 57)

The following procedure should be used when constructing a command string.
1. The first two to three characters of the command string must consist of the
Address Command (N) and the address number of the unit (0-99). If the
unit address is zero, the address command and number need not be sent.
2. The next character in the command string is the command that the unit is to
perform (P, R, T, C, or V).
3. A Value Identifier is next if it pertains to the command. The command P
(print) does not require a Value Identifier.
4. The numerical data is next in the command string if the “Change Value” or
“Control Action” command is used.
5. All command strings must be terminated with an asterisk * (2AH). This
character indicates to the unit that the command string is complete and the
unit begins processing the command.
Below are typical examples of command strings.
Example: Change Proportional Band Value to 13.0% on the unit with an
address of 2.
Command String: N2VD130*
Example: Transmit the Input Display Value of the unit with an address of 3.
Command String: N3TA*
Example: Reset Alarm Output 1 of the unit with an address of 0.
Command String: RG*
If illegal commands or characters are sent to the PCU, the string must be
re-transmitted.
When writing application programs in BASIC, the transmission of spaces
or carriage return and line feed should be inhibited by using the semicolon
delimiter with the “PRINT” statement. The unit does not accept a carriage
return or line feed as valid characters.
It is recommended that a “Transmit Value” command follow a “Change
Value” Command. If this is done, the reception of the data can provide a
timing reference for sending another command and insures that the change
has occurred. When a “Change Value or Reset” command is sent to the unit,
there is time required for the unit to process the command string. Figure 22,
Timing Diagrams, shows the timing considerations that need to be made.
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Figure 22, Timing Diagrams