West Control Solutions N8100 - Manual (Page 29)

3.2.4 Type 1 Message
L {N} ? ? *
This message is used by the master device to determine whether the addressed
slave Controller is active. The reply from the slave Controller, if it is active, is
L {N} ? A *
An inactive Controller will give no reply.
3.2.5 Type 2 Message
L {N} {P} {C} *
This type of message is used by the master device to interrogate or modify a
parameter in the addressed Controller. {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 Controller is of the form:
L {N} {P} {DATA} A *
where {DATA} comprises five ASCII-coded digits whose format is shown in Table
3-1. 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 Controller replies with
a negative acknowledgement:
L {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 Controller, the reply is
L{N}{P}<??>0A* if the process
variable is over-range, or L{N}{P}<??>5A* if the process variable is
under-range.
Scan Tables
A parameter identifier character “]” in the message from the master device
indicates that a “Scan Table” operation is required. This provides a facility for
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