Applies To:
  • CitectSCADA
  • CitectHMI

Question. I am using COMx driver. I have noticed that my I/O devices do not come back online after the COMx has faulted. This fault can occur due I/O device losing the main power or I/O devices getting shut down. When the power is restored to these devices, they never come back online. Only way to bring them bak online is to restart CitectSCADA. Why? 

Answer: COMX driver shuts itself down when the power to the I/O devices go down.

You can also get errors like " "ComX readCommBlock status == FALSE: Error 'The I/O operation has been aborted because of either a thread exit or an application request (0x3e3)' " when the power is restored to the IO devices.

COMx will not restart or reinitialise until you restart CitectSCADA. You can use -nt or -nts switches in special options of COMx port to get around this problem.

Below is some explanation on these switches


With some serial interfaces, line faults can cause the COMX read thread to shutdown. This meant the driver would not recover after the fault. With the -nt option (no terminate), the thread is NOT shutdown. This allows the system to recover.


Do not terminate at startup if errors occur. Keep retrying to init the driver .For this to work, the driver must do a COMReset in its InitUnit() code, or Cicode should be doing this.