Despatch P1400+ Temperature Controller - Manual (Page 73)

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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.
11.4 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.