470 Rockwell Automation Publication 1756-RM003N-EN-P - October 2011
Chapter 11 Program Control Instructions (JMP, LBL, JSR, RET, SBR, JXR, TND, MCR, UID, UIE, AFI, NOP, EOT, SFP, SFR, EVENT)
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.
Operands:
Relay Ladder
None
Structured Text
None
You must enter the parentheses () after the instruction mnemonic, even though
there are no operands.
Description: 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.
Follow these steps to prevent a series of rungs from being interrupted.
1. 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.
2. Above the first rung that you do not want interrupted, enter a rung and a
UID instruction.
3. After the last rung in the series that you do not want interrupted, enter a
rung and a UIE instruction.
4. If required, you can nest pairs of UID/UIE instructions.
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