Despatch P1400+ Temperature Controller - Manual (Page 72)

66
Type 2 Message
L {N} {P} {C} * or R {N} {P} {C} *
This type of message is used by the master device, to interrogate or modify a parameter in the
addressed slave device. {P} identifies the parameter and {C} represents the command to be
executed, which may be one of the following:
+ (Hex 2B) = Increment the value of the parameter defined by {P}
– (Hex 2D) = Decrement the value of the parameter defined by {P}
? (Hex 3F) = Determine the current value of the parameter defined by {P}
The reply from the addressed slave device is of the form:
L {N} {P} {DATA} A * or R {N} {P} {DATA} A *
where {DATA} comprises five ASCII-coded digits whose format is shown in the Data Element table
above. The data is the value requested in a query message or the new value of the parameter after
modification. If the action requested by the message from the master device would result in an
invalid value for that parameter (either because the requested new value would be outside the
permitted range for that parameter or because the parameter is not modifiable), the slave device
replies with a negative acknowledgement:
L {N} {P} {DATA} N * or R {N} {P} {DATA} N *
The {DATA} string in the negative acknowledgement reply will be indeterminate. If the process
variable or the deviation is interrogated while the process variable is outside the range of the slave
device, the reply is:
L {N} {P} < ? ? > 0 A *
if the process variable is over-range, or
L {N} {P} < ? ? > 5 A *
if the process variable is under-range.
Type 3 Message
L {N} {P} # {DATA} * or R {N} {P} # {DATA} *
This message type is used by the master device to set a parameter to the value specified in
{DATA}. The command is not implemented immediately by the slave device; the slave will receive
this command and will then wait for a Type 4 message (see below). Upon receipt of a Type 3
message, if the {DATA} content and the specified parameter are valid, the slave device reply is of
the form:
L {N} {P} {DATA} I * or R {N} {P} {DATA} I *
(where I = Hex 49) indicating that the slave device is ready to implement the command. If the
parameter specified is invalid or is not modifiable or if the desired value is outside the permitted
range for that parameter, the slave device replies with a negative acknowledgement in the form:
L {N} {P} {DATA} N * or R {N} {P} {DATA} N *