In fact function 5 (write single %M) is not present in ESME V1.1.
Because It was an error of SoMachine V4.3 documentation, function 5 is not available on M251 modbus slave in all versions (SoMachine and ESME).
Workaround:
A possible workaround is to do a write single register - %MW (FC6).
in the controller program, you have to store this %MW in a variable and after you can read all bit of this variable with war.0, var.1....(see attached picture)
Released for:Schneider Electric Nigeria