Modbus TCP Input bits on Modicon M340

[ltavolari]

I'm new in schneider world and I have a question.

I'm using my modicon as a Modbus TCP Server, my client use for data exchange:

Holding Registers (%MW from 0 to 20): Client transmit data to Server on these addresses

Input Bits (%I from 0 to 😎 : Client Read data from Server on these addresses

Coils (%M from 0 to 8): Client transmit bit to Server on these addresses

When I use Topological Memory Management, Coils and input bits are both on %M.

When I use Mixed topological and State RAM Memory management, I read Coils on %M, but I can't write on %I, because it are Read only bits.

Is this the normal behavior or I'm doing something wrong?

[AlastairF]

Traditional ModBus addressing vs IEC ModBus addressing

In all cases, note that the traditional ModBus address starts at 1 and the IEC ModBus address starts at 0.

Input bits 1xxxx1 become %1xxxx0

Input words 3xxxx1 become %IWxxxx0

Output bits 0xxxx1 become %Mxxxx0

Output words 4xxxx1 become %MWxxxx0

Input bits and input words can only be read by an external device.

If you wish to simulate/ manipulate these values in your application you can do this using the Simulation function blocks.
Refer to the Help file for WRITE_INPUT_EBOOL as an example.

Output bits and output words are Read/ Write capable.