Type 2 Message; Type 3 Message - WEST P8700 User Manual

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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
above. The data is the value requested in a query message or the new value of the
table
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 whilst 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:
59305, Issue 5 – March 2005
- DIN Controllers & Indicators - Product Manual
ASCII Communications
Data Element
Page 101