User Interrupt Disable (UID)/User Interrupt Enable (UIE)
The UID instruction and the UIE instruction work together to prevent a small number of critical rungs from being interrupted by other tasks.
When the rung-condition-in is true, the:
- UID instruction prevents higher-priority tasks from interrupting the current task, but does not disable execution of a fault routine or the Controller Fault Handler.
- UIE instruction enables other tasks to interrupt the current task.
To prevent a series of rungs from being interrupted:
- Limit the number of rungs that you do not want interrupted to as few as possible. Disabling interrupts for a prolonged period of time can produce communication loss.
- Above the first rung that you do not want interrupted, enter a rung and a UID instruction.
- After the last rung in the series that you do not want interrupted, enter a rung and a UIE instruction.
- If required, you can nest pairs of UID/UIE instructions.
When the UID is called for the first time, it bumps priority, saves the old priority, and increments a nesting counter. Each subsequent call increments the count. The UIE will decrement the nesting counter. If the new value is 0, it will restore the saved priority.
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Ladder Diagrams
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FactoryTalk Design Studio
DSL - Ladder DiagramUID();
UIE();
Affects Math Status Flags
No.
Major/Minor Faults
None specific to this instruction. See Common Attributes for operand-related faults.
Execution
Ladder Diagram
Condition/State | Action |
|---|---|
Prescan | N/A |
Rung-condition-in is false | N/A |
Rung-condition-in is true | The UID instruction prevents the containing user task from being Interrupted. The UIE instruction enables the containing user task to be interrupted as is normally in the case. |
Postscan | N/A |
Example
Ladder Diagram
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