Applies To:
  • CitectSCADA 6.xx
  • CitectHMI 6.xx
Summary:
If you defined your data block as a Long datatype in the PSDirect backend (and in CitectSCADA you have defined the tag to be that of Long data type as well), CitectSCADA can read the value off the Siemens S5 PLC but CitectSCADA won't write to the Siemens S5 PLC correctly.
 

Solution:
The PSDIRECT front end driver is designed to work with only Word(KF) backend blocks, it then translates & aggregates to LONG & REAL.  This allows backend blocks spanning many datatypes.

The creator of this driver (ProScada) will remove those datatypes (other than Word) in the next version.

At the time of the writing this KB article the current version of PSDirect backend is:

Ethernet backend ver 7.9.51.005
MPI backend ver 7.9.06.000

If you need to read and write to your S5 PLC which has a Long datatype, you can create a datablock (e.g. DB:206:0 - DB:206:3) of Word datatype in the PSDirect backend, then define a tag of Long datatype in CitectSCADA as the backend block can span the entire DB and include any frontend datatype.

Remember when using LONGs:

- The last address in the backend block must be 1+ the highest Frontend address
- Beware the CitectSCADA alignment restriction, if the first LONG is an even address then ALL of them must be even
 
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