Thermo Electron Corporation 42i Low Source Instruction Manual C-1
Appendix C MODBUS Protocol
This appendix provides a description of the MODBUS Protocol Interface
and is supported both over RS-232/485 (RTU protocol) as well as TCP/IP
over Ethernet.
The MODBUS Commands that are implemented are explained in detail in
this document. The MODBUS protocol support for the iSeries enables the
user to perform the functions of reading the various concentrations and
other analog values or variables, read the status of the digital outputs of the
analyzer, and to trigger or simulate the activation of a digital input to the
instrument. This is achieved by using the supported MODBUS commands
listed below.
For details of the Model 42i Low Source MODBUS Protocol specification,
see the following topics:
• “Serial Communication Parameters” on page C-2 describes the
parameters used to support MODBUS RTU protocol.
• “TCP Communication Parameters” on page C-2 describes the
parameters used for TCP connection.
• “Application Data Unit Definition” on page C-2 describes the formats
used over serial and TCP/IP.
• “Function Codes” on page C-3 describes the various function codes
supported by the instrument.
• “MODBUS Commands Supported” on page C-8 lists the MODBUS
commands supported in Table C-1 through Table C-3.
Additional information on the MODBUS protocol can be obtained at
http://www.modbus.org
. References are from MODBUS Application
Protocol Specification V1.1a MODBUS-IDA June 4, 2004.
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