Applies To:
  • CitectSCADA
  • S7NT driver version

If an S7 PLC is overloaded or under very heavy load it is possible for the S7NT driver to send more that 2 commands to the S7 API at once. This causes the S7 API to return error 0x227a which the S7NT driver returns to CitectSCADA as a driver error.

After this has occurred or when timeouts occur it is possible for the S7NT driver to get out of sync with the S7 API. This can lead to the channel being forced offline.

This problem has been fixed in version of the S7NT driver.

Citect has also observed issues relating to the connection cleanup in SoftNet. We would recommend that if CitectSCADA is restarted more than twice that the computer be restarted to clear the connection handling in SoftNet.

This can manifest itself as the channel repeatedly coming online (reported in the kernel) without processing any requests between channel online events.

S7 S7NT driver timeout unit channel offline