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Modbus protocol for Mitsubishi AJ71UC24
Implementation of Mitsubishi Modbus protocol.

I am trying to implement a modbus protocol to communicate with a mitsubishi A3U PLC. After reading the manual, I have some difficulty to deduce the definition of the frame formation.

For standard Function (Eg. 01,02,03,etc)
- How to derive the "Device designation" code for a particular device such as X,Y,D,etc?

For Optional function code (Code 65-75)
- It is mentioned in the manual that the function 70 can be changed via some setting. If the function code is changable, how can I know what my current PLC is using for this function?
- What is the PC number in the message format?
- Is the Address refer to ID set on the AJ71UC24 in the message format?

I will try to implement the comm. code in Labview. Is there anyone who had build these type of code (Mitsubishi Modbus) before?

Thank you.



We do have MODBUS Master drivers that can be used for your purpose. It support all the function codes defined by MODBUS standards apart from the commonly used function codes like 01,02,03,04,05,06,15 and 16. These drivers support serial networks like RS232 and RS485 and also TCP/IP networks. Each of the MODBUS device will be having a unique ID with which it will be identified in the network. First byte in the MODBUS frame is used for this id. These drivers are very easy to use and can be integrated to any of the automation packages, in your case LabView. You can get more info about this at or you can mail me too.


Using module AJ71UC24-S2, it's a modbus module.