Page 104 - Gas Detection Systems Training Manual

General Description
About The SEC 3120 Digital Gas Transmitter
The SEC 3120 Digital Gas Transmitter is the latest generation Gas Transmitter from Sensor Electronics Corporation, and is fully compatible
with its predecessor, the SEC 3100. The SEC 3120 Digital Gas
Transmitter allows multiple single and multi-channel SEC
sensors to be connected to it and acts as a central
communication, control, status and data logging hub for them.
While the SEC 3100 did not provide full 16-bit standard
Modbus (PI-MBUS-300 Rev. J. compliance) support, the
special SEC 3100MB16 does and is compatible with the SEC
3120 which provides full (relevant) compliance and major
feature and sensor consolidation capabilities, as well as optional sensor redundancy.
SEC 3120 Modbus Standard Supported
The SEC 3120 Digital Gas Transmitter supports master mode communication as a Modbus RTU slave. While it supports other Modbus interfaces, this document addresses the specific 16-bit standard Modbus protocol as described in the Modicon Modbus Specification PI-MBUS-300 Rev. J. The reader should familiarize themselves with this document to fully understand and utilized this Modbus interface.
16-bit Modbus Supported Features and Functions Overview
Functions Codes -
03 - Read Multiple Holding Registers (supported fully)
06 - Preset Single Holding Register (supported fully)
16 - Preset/Write Multiple Holding Registers (supported fully) 01 - Read Coils (not supported)
05 - Force Single Coil (not supported)
15 - Force/Write Multiple Coils (not supported)
07 - Read Exception Register (not supported)
Broadcast (Network ID 0) for all other function codes is not supported, except for Preset (code 06) Holding Register 42920 (Listen Only Modbus Mode) and 42921 (Resume from Listen Only Modbus Mode).
All other function codes are not supported for broadcast mode in this interface.
SEC 3120 16-bit Modbus Manual Page 3 Of 46 Sensor Electronics Corporation For Version 1.2 and above December 2012 P/N 1580282, Rev. 1, 20121228