Issue

Values are not updated correctly when a Modbus TCP client using Unit ID = 255 communicates to a BMXNOC0401 acting as server  to read M340 Holding Registers.

Product Line

Modicon M340 + BMXNOC0401 Ethernet Communication Module.

Resolution

For some Modbus TCP devices, Unit ID such as 100 or 255 are reserved for accesing Ethernet diagnostic data via Modbus TCP (via Modbus FC03 “Read Holding Registers”). Refer to the Modicon M580 platform topic Diagnostics Available through Modbus/TCP (see Modicon M580, Hardware, Reference Manual) for additional information.

When accessing diagnostic data from the BMXNOC0401 Ethernet communication module itself, use Unit ID = 255.

When accessing data in the application running in the PLC (e.g., M340 %MWs : Holding Registers), use a value between 0 and 254 (Unit ID =1 is recommended).

Released for: Schneider Electric South Africa