Applies To:
  • CitectSCADA 5.10, 5.20
Summary:
Incorrect results may occur when using the CtApi function ctListData to read digital tags from a list. This problem may also effect OPC clients as the Citect OPC server uses the same functions to read data from Citect.

This will happen when digitals in the list, which can be blocked, span a 16 bit boundary. The only time that it will currently give correct results is if the lowest digital point in the block is on a 16 bit boundary.

For example, consider a list for the generic protocol of digital tags with addresses:

D30, D31, D32, D33, D34, D35

D33-35 will read incorrectly. But if the same list also had D17, then all will read correctly.

 

Solution:
CIT has confirmed this to be a problem in Citect for Windows versions 5.10 to 5.20. This problem has been fixed in version 5.21.  If possible, you can correct the situation by always making sure that the digital point in the list with the lowest address is on a 16 bit boundary. 
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