Allen-Bradley 1756-CNB User Manual page 86

86 Configure and Program the Controller
Publication 1756-UM523F-EN-P - December 2006
Use UID and UIE Instruction Pairs
Bound critical rungs with UID and UIE instruction pairs. This prevents
the higher priority task form interrupting the scan-dependent logic.
Buffer Critical Data
This example shows the use of a buffer together with a BSL
instruction.
1.
1. The COP instruction moves the data into a buffer array.
2. The BSL instruction uses the data in the buffer. If a switchover
occurs, the source data (array tag) remains unaffected.
3. The CPS instruction updates array tag. Since higher priority
tasks cannot interrupt a CPS instruction, the instruction keeps
the integrity of the data.
2. 3.
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