Applies To:
  • CitectSCADA


It is important to be as efficient as possible in the way the PLC is programmed. The following is from the Allen Bradley/Rockwell Automation website. Please refer to KB article number ‘A54732518 - Optimizing a ControlLogix Redundancy System, Programming Guidelines and Case Study’ for more information regarding other good programming practices.


Item 8: Layout of User Defined Structures

How you layout a UDS determines how many bytes of memory it will take. Care should be taken when laying out UDSs. Looking at the example below shows by moving one BOOL saves 4 bytes. When laying out UDS group data types within the UDS. All elements in a structure are located on byte boundaries.

By careful when laying out the structure of a UDS. The more compact a UDS is the smaller tag database and therefore a reduction in the size of crossloads. This will result in faster program execution.


Please refer to Citect KB article titled “Recommended programming practices for optimal performance of Citect’s ABCLX Driver” for information on how to optimize the performance of Citect’s ABCLX driver.



ABCLX, UDT, UDS, Structure, Structures, communication, bit access