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

When communicating via RS232 with a Koyo Direct Logic PLC using the CCM protocol, the following errors were logged to the syslog.dat file and also displayed in the Kernel:

Generic 000006 Response bad or garbled
Driver 00000002 (0x00000002) Parity error

Generic 000007 I/O Device not responding
Driver 00000021 (0x00000015) Timeout error

Generic 000012 I/O Device off-line, cannot talk
Driver 00000023 (0x00000017) I/O Device not on-line

The Koyo Direct Logic PLC was installed in a Cabinet that also included several VSDs and Drives. So it is expected that there are many communications errors, and noise related problems.

Slowing down the baud rate did not reduce the rate of error.


The solution to this problem was to modify the following parameter:


By default the value of MaxPending is 8. This means that the driver can have up to 8 outstanding requests. This does put more pressure on the driver to handle timeouts and retry requests for 8 different communication requests.

Reducing the number of MaxPending to 2 allows the driver to recover when communications errors do occur.


CCM, Koyo, Communications errors, Direct Logic, 0x00000017, 0x00000015, 0x00000002, noise