About The Program Flow Control Instructions; Jump (Jmp) And Label (Lbl) - Allen-Bradley MicroLogix 1000 User Manual

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MicroLogix 1000 Programmable Controllers User Manual
Preface

About the Program Flow Control Instructions

Use these instructions to control the sequence in which your program is executed.

Jump (JMP) and Label (LBL)

Use these instructions in pairs to skip portions of the ladder program.
(JMP)
]LBL[
True
Execution Times
(µsec) when
:
True False
False
JMP 9.04 6.78
LBL 1.45 0.99
Jumping forward to a label saves program scan time by omitting a program segment
until needed. Jumping backward lets the controller execute program segments
repeatedly.
Note
Be careful not to jump backwards an excessive number of times. The watchdog
timer could time out and fault the controller. Use a counter, timer, or the "program
scan" register (system status register, word S:3, bits 0–7) to limit the amount of time
you spend looping inside of JMP/LBL instructions.
Entering Parameters
Enter a decimal label number from 0 to 999. You can place up to 1,000 labels in
each subroutine file.
Using JMP
The JMP instruction causes the controller to skip rungs. You can jump to the same
label from one or more JMP instruction.
10–2
If the Rung Containing the
Jump Instruction is:
Then the Program:
Skips from the rung containing the JMP instruction to the rung
containing the designated LBL instruction and continues
executing. You can jump forward or backward.
Does not execute the JMP instruction.