OxyDetect Oxygen Deficiency Gas Detector
Appendix
05311001B / Revision 4
67
A3
IMPLEMENTATION GUIDE FOR MODBUS ETHERNET
COMMUNICATIONS (OPTION)
A3.1 Introduction
This appendix details the implementation and use of the Modbus protocol in the
Servomex OxyDetect.
A3.2 References
Document "MODBUS over Serial Line Specification & Implementation guide V1.0
Nov 02" Modbus web site
modbus.org
.
A3.3 Supported function codes
For simplicity, only the following function codes will be supported.
Function
Description
Usage
01
Read coils
Read calibration status, etc.
02
Read discrete inputs
Read faults and alarm states.
03
Read holding registers
Read settings.
04
Read input registers
Read measurements, units, etc.
05
Write single coil
Change modes, perform calibration etc.
06
Write single register
Change single setting.
08
Sub Function
00 = Return
query data
Diagnostic to test communications.
16
Write multiple registers
Change multiple settings.
A3.4 Exception codes
If an error should occur while processing a message one of the following exception
codes will be returned by the instrument.
Code
Condition
Meaning
01
Illegal function
Requested function code is not supported.
02
Illegal data address
The combination of data address and transfer
length is invalid for this function.
03
Illegal data value
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.