MODBUS Function code


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I have requirement of ADDRESS, WORD, BIT - For (DI-30001.0,30001.1,30001.2…….) and for DO(40001.0,40002.0,40003.0) for AI(30027,30028,30029)

• LENGTH (BIT, BYTE, WORD), I have to show the unit with the digit like 1 BIT or 1 byte

As per Universal standard for MODBUS, Function code 3 is for Holding register which support read/write and Function code 4 is for Input register which support read only. So it seems above DO at Function code 4 will not support.

Could you please clarify above?