My situation: S7-1200 is modbus master and software Modbus Slave is slave (modbus poll). I configure MB_MASTER according to manuals and forums and write registers into slave (without problem, MODE=1). But if i change MODE=1 to MODE=0, nothing will happen. PLC don't read registers from slave, because BD in DATA_PTR don't change.

Modbus frames from slave are correct. It seems PLC understands but don't save slave's answer into global DB.