Sensor Electronics SEC 3000, Instruction And Operation Manual

Page: 360 / 489

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
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.