Logix5000 Controllers General Instructions - SLAC Confluence

436 Program Control Instructions (JMP, LBL, JSR, RET, SBR, JXR, TND, MCR, UID, UIE, AFI, NOP, EOT, SFP, SFR, EVENT)Jump to Label (JMP)Label (LBL)The JMP and LBL instructions skip portions of ladder logic.Operands:Relay LadderOperand Type Format DescriptionJMP instructionLabel name label name enter name for associated LBL instructionLBL instructionLabel name label name execution jumps to LBL instruction withreferenced label nameDescription:When enabled, the JMP instruction skips to the referenced LBLinstruction and the controller continues executing from there. Whendisabled, the JMP instruction does not affect ladder execution.The JMP instruction can move ladder execution forward or backward.Jumping forward to a label saves program scan time by omitting alogic segment until it’s needed. Jumping backward lets the controllerrepeat iterations of logic.Be careful not to jump backward an excessive number of times. Thewatchdog timer could time out because the controller never reachesthe end of the logic, which in turn faults the controller.ATTENTIONJumped logic is not scanned. Place critical logic outside thejumped zone.The LBL instruction is the target of the JMP instruction that has thesame label name. Make sure the LBL instruction is the firstinstruction on its rung.A label name must be unique within a routine. The name can:• have as many as 40 characters• contain letters, numbers, and underscores (_)Publication 1756-RM003I-EN-P - January 2007