Page 122 - Gas Detection Systems Training Manual

Holding Register Address
Read or Write
Sensor Register Description (See Parameter Table for specifics)
42x28 -x 30
Read/Write
Calibration Value (IEEE 754 32-bit float)
42x31 -x32
Read
Sensor Range (IEEE 754 32-bit float)
42x33
Read
Alarm Configuration (bit map)
42x34 - x37
Read
Gas Name (ASCII characters eight, 1st left to right)
42x38 - x39
Read
Gas Units Name (ASCII characters four, 1st left to right)
42x40
Write Only
Start Self Test (with password)
Table 4: Region 9: 3120 Unit Registers
Holding Register Address
Read or Write
3120 Unit Register Description (See Parameter Table for specifics)
42901
Read
Unit Operating Status (bit map)
42902 - 03
Read
Fault Relay Reason Code (32-bit bit map)
42904 - 05
Read
Unit Serial Number (32-bit integer)
42906 - 11
Read
Clock Read Registers (real-time)
42912 - 17
Write Only
Clock Write Registers (New write hold registers)
42918
Write Only
Set Clock from New Clock write hold registers
42919
Write Only
Diagnostics (force alarm/fault relays, force LED blinking)
42920
Write Only
Set Unit into Listen Only Modbus Mode
42921
Write Only
Restore Unit back from Listen Only Modbus Mode
42922
Read
Maximum number of sensors that can be attached
42923
Read
Unit Type Code
42924 - 25
Read
Unit Firmware Version (2- words for major.minor.build)
Modbus Protocol
Introducing Modbus Protocol
Modbus communication is based on a master slave technique, in which only one device (the master) can initiate transactions (queries). The other devices (the slaves) respond by supplying the requested data to the master, or by taking the action requested in the query. The master can address individual slaves or can initiate a broadcast message to all slaves. Slaves return a message (a response) to queries that are addressed to them individually. Responses are not returned to broadcast queries from the master.
The Modbus protocol establishes the format for the master s query by placing the device (or broadcast) address, a function code defining the requested action, any data to be sent and an error-checking field into the message. The slave s response message is also constructed using Modbus protocol. The response contains fields confirming the action taken, any data to be returned and an error-checking field. If an error occurred in receipt of the message, or if the slave is unable to perform the requested action, the slave will construct an error message and send it as the response.
SEC 3120 16-bit Modbus Manual Page 21 Of 46 Sensor Electronics Corporation For Version 1.2 and above December 2012 P/N 1580282, Rev. 1, 20121228