PLC ABB Ac500 Pm571 As Modbus Slave


Thread Starter

Roberto ZENI


I have a Master PLC that must talk to the PLC in question (ABB PLC is Modbus Slave).

Now I must write the "communication table" and I dont know if the PLC ABB has separate areas for Holding Register, Coil Status, Input and Input Status Register, or has one area on which the Master can read/write using with different views using different FC ModBus)

Basically I have to validate two Hypothesis

Hypothesis 1
the contents of the "Holding register 0 (40001)" has no correlation with the contents of the "Input Status 0 (10001)" rather than with "Coil Status 0 (1)" or "Input Register 0 ( 30001)"

Hypothesis 2
If, for example, the contents of the "Holding register 0 (40001)" is HFFFF is also the content of the "Input Register 0 (30001)" will be the same and the contents of the "Input Status number 0 (10001)" and "Coil Status 0 (1)" will be equal to 1.

Analyzing the ModBus specification (and also from previous experience) I realized that both behaviors are appropriate standard ModBus and depend on the element which is carried by the implementation Slave (which, unfortunately, but I do not know the technical characteristics).