Logix5000 Controllers General Instructions - SLAC Confluence

456 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 preventa small number of critical rungs from being interrupted by other tasks.Operands:Relay LaddernoneUID();UIE();Structured TextnoneYou 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 interruptingthe current task but does not disable execution of a fault routineor the Controller Fault Handler.• UIE instruction enables other tasks to interrupt the current task.To prevent a series of rungs from being interrupted:1. Limit the number of rungs that you do not want interrupted to asfew as possible. Disabling interrupts for a prolonged period oftime can produce communication loss.2. Above the first rung that you do not want interrupted, enter arung 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.Arithmetic Status Flags:Fault Conditions:not affectednonePublication 1756-RM003I-EN-P - January 2007