West Control Solutions 8700+ - Manual (Page 135)

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ASCII Communications 59305, Issue 7 – March 2014
Type 4 Message
L {N} {P} I * or R {N} {P} I *
This type of message is sent by the master device to the addressed slave device, following a
successful Type 3 transaction with the same slave device. Provided that the {DATA} content
and the parameter specified in the preceding Type 3 message are still valid, the slave device
will then set the parameter to the desired value and will reply in the form:
L {N} {P} {DATA} A *
where {DATA} is the new value of the parameter. If the new value or parameter specified is
invalid, the slave device will reply with a negative acknowledgement in the form:
L {N} {P} {DATA} N *
where {DATA} is indeterminate. If the immediately preceding message received by the slave
device was not a Type 3 message, the Type 4 message is ignored.
Error Response
The circumstances under which a message received from the master device is ignored are:
Parity error detected
Syntax error detected
Timeout elapsed
Receipt of a Type 4 message without a preceding Type 3 command message.
Negative acknowledgements will be returned if, in spite of the received message being
notionally correct, the slave device cannot supply the requested information or perform the
requested operation. The {DATA} element of a negative acknowledgement will be
indeterminate.