MTR-3 Installation Instructions
DEIF A/S Page 29 of 51
7. Appendix A: Modbus protocol
Modbus communication protocol
Modbus is enabled via RS485 or USB. The response is the same type as the request.
Two versions of Modbus register tables are available:
• VERSION 1: MTR-3 Modbus registers
• VERSION 2: Compatibility with previous version of the product, the MTR-2
Modbus
Modbus protocol enables operation of device on Modbus networks. For device with serial
communication, the Modbus protocol enables point-to-point (for example device to PC) multi-drop
communication via RS485 communication. Modbus protocol is a widely supported open
interconnect originally designed by Modicon.
The memory reference for input and holding registers is 300001 and 400001 respectively.
The register tables no the next pages shows both the PLC address and Modbus address to read
from the desired register.
Example for reading Frequency parameter:
PLC: Read address 300106-300107
Modbus: Read address 105-106 with function 4
The Modbus address will always be 1 lower than the PLC address because PLC addresses starts
with 1 where Modbus addresses starts with 0.
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