Simulate IR and DI

[Diogo Oliveira]

Hello, I'm trying to simulate a modbus server with pymodbus, and need to update the values of IR and DI registers, while the program is working. For example, it would turn on/turn off a DI and increment an IR.

Is there any way to do this without changing the code of my client device?

My guess would be to define some function codes to write to those registers, but still haven't made much progress.

[Sanjay KV]

Look in to updating server example https://pymodbus.readthedocs.io/en/latest/source/example/dbstore_update_server.html

ಬುಧ, ಜನವರಿ 19, 2022 21:16 ದಿನಾಂಕದಂದು Diogo Oliveira <doli...@eneida.io> ಅವರು ಬರೆದಿದ್ದಾರೆ:

Hello, I'm trying to simulate a modbus server with pymodbus, and need to update the values of IR and DI registers, while the program is working. For example, it would turn on/turn off a DI and increment an IR.

Is there any way to do this without changing the code of my client device?

My guess would be to define some function codes to write to those registers, but still haven't made much progress.

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[Diogo Oliveira]

That really doesn't help me because in that example they use the writeFunction = 0x10 and readFunction = 0x03. But that, on the modbus specification, are the function codes for writing to and reading from a holding register. 
I'm looking to be able to do that to discrete inputs and input registers, as I'm trying to simulate a server that randomly updates its values.

[Diogo Oliveira]

I figured out a simple solution, just in case someone needs this in the future.

The way I solved this was by adding custom messages which mimic the behavior of writing to a coil or input register.

And don't forget to add your custom message as an argument when starting the server.

I followed the source code for writing to a coil: https://github.com/riptideio/pymodbus/blob/master/pymodbus/bit_write_message.py, and just changed to write to a discrete input. That way I can manipulate those registers how I want to simulate the behavior of a physical modbus server device.