Hi,
I've the same problem, I've connected the device with my PC, where I have a application that sends Modbus commands. The format that I send is as follows:
0103xxxx0001<CRC16> <CRC16>
01 - for slave number 1
03 - read holding registers
xxxx - the address of the register
0001 - read 1 register
I got an answer from the PLC, but it is always "0".
I have value in DM(x) register
Regards,
Julian Dimitrov