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.

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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.

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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.