Applies To:
  • CitectSCADA 5.xx, 6.xx
  • CitectHMI 5.xx, 6.xx
Summary:
I am using the PSDirect driver to communicate to my S7 series PLC and I am seeing intermittent #COMs every few minutes. I also get the following error in the syslog.dat file:

Error: Unit offline
READ Generic 000012 Driver 00000266 (0x0000010e)

What is the cause of this error and how do I correct this error?
 

Solution:
When using the PSDirect driver, only 1 port is required on the IO server, even if different PLC types S5/S7 are being used. Performance is just as good with only 1 port because the driver is reading instantly from a cache. When more than 1 port is used, the intermittent #COM problem can occur. Removing and using only 1 port will resolve the issue.

Note:
The Intent of this error is to indicate that that backend polling program has stopped running.  You can trigger it by killing the process "SIXSPOLL.EXE" in taskmanager.
This issue has been improved with respect to >1 channel/ports to the extent that this error should be viewed as a bug if the driver is running normally. Please make sure that you are running at least V2.4.3 of the frontend, as versions ~2.1-2.3 may throw this error spuriously. 
 
Keywords:
PsDirect, #COM, Intermittent, 10e, 0x10e,266 

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