Applies To:
  • CitectSCADA 5.xx, 6.xx
  • CitectHMI 5.xx, 6.xx

I cannot get successful communications to my HITACHI PLC. When I turn on driver debugging ([HITACHI]debugstr=* ALL) I see that CitectSCADA is sending requests and receiving responses but then after a couple of cycles of this, CitectSCADA will send a request and no response will be received by the timeout period ([HITACHI]Timeout). When a retry is issued, the PLC will respond correctly for a few more responses and then fail again. This happens in a continuous loop.

You need to use the -h special option in your COMX port.

-h Data will be transmitted only when CTS is high.

When communicating with the Hitachi PLC, you must use a communications board that is capable of buffering the data. The Hitachi PLC has a slow communications port. The best card to use for CitectHMI/SCADA is a Digiboard, preferably a PCXI or a PCXE. You might be able to use a serial port equipped with a 16550A UART. 

HITACHI, communications, #COMS