MultiExact Gas Analyser Appendix
A3.4 Supported function codes
For simplicity, only the following function codes will be supported.
Read calibration status, pump state, etc.
Read faults and alarm states.
Read measurements, units, etc.
Change modes, perform calibration etc.
00 = Return
Diagnostic to test communications.
Change multiple settings.
A3.5 Exception codes
If an error should occur while processing a message one of the following exception
codes will be returned by the instrument.
Requested function code is not supported.
The combination of data address and transfer
length is invalid for this function.
A value contained in the query data field is not an
allowable value. This indicates a fault in the
structure of the remainder of a complex request.
This does NOT mean that a value to be stored in a
register is incorrect as Modbus has no means of
determining what is legal for any particular register.
An unrecoverable error occurred while the unit was
attempting to perform the requested action.
A3.6 Addressing
Addresses in Modbus ADU (application data unit), run from 1 – N, whereas addresses
in the Modbus PDU (protocol data unit) run from 0 – N. This appendix gives addresses
in the ADU model. Depending on the particular Modbus master, addresses may have
to be entered as they are given or have 1 subtracted from them. For example to read
register 101 an address of 100 may be needed.
05410001A / Revision 6 105
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