Logix5000 Controllers General Instructions - SLAC Confluence

Program Control Instructions (JMP, LBL, JSR, RET, SBR, JXR, TND, MCR, UID, UIE, AFI, NOP, EOT, SFP, SFR, EVENT) 457Execution:Condition Relay Ladder Action Structured Text Actionprescan The rung-condition-out is set to false. No action taken.rung-condition-in is false The rung-condition-out is set to false. narung-condition-in is true The instruction executes.naThe rung-condition-out is set to true.EnableIn is set na EnableIn is always set.instruction executionThe instruction executes.The UID instruction prevents interruption by higher-priority tasks.The UIE instruction enables interruption by higher-priority tasks.postscan The rung-condition-out is set to false. No action taken.Example:When an error occurs (error_bit is on), the FSC instruction checks theerror code against a list of critical errors. If the FSC instruction findsthat the error is critical (error_check.FD is on), an alarm isannunciated. The UID and UIE instructions prevent any other tasksfrom interrupting the error checking and alarming.Relay LadderUIDerror_bitFSCFile Search/CompareControlerror_checkLength 10Position 8ModeALLExpression error_code=error_list[error_check.POS]ENDNERerror_check.FDalarmUIEStructured TextUID();UIE();Publication 1756-RM003I-EN-P - January 2007