Rockwell Automation 1772-LV Mini-PLC - 2/15 Programmable Controller (Series B) Programming and Operations - Manual (Page 65)

Advanced Instruction Set
Chapter 6
6Ć8
Section B
Program Control Instructions
Certain applications may need programming techniques designed to override a
group of non-retentive outputs or update I/O ahead of the usual I/O scan time.
The program control instructions satisfies this need.
Program control instructions are divided into two categories:
Output Override
Immediate I/O Update
The table below illustrates specific instructions for these categories:
Program Control Instructions
Output Override Immediate Update I/O
Master Control Reset Immediate Input Update
Zone Control last State Immediate Output Update
The output override, or zone type instructions, operate similar to a hardwired
master control relay in that they can affect a group of outputs in the user
program. But these instructions not a substitute for a hardwired master control
relay, which provides emergency I/O power shutdown.
Master Control Reset
Symbol: -(MCR)-
Purpose: Controls a group of outputs.
Syntax: Two instructions are required: (Figure 6.3)
To begin the zone (start fence)
To end the zone (end fence)
Program the start fence with a set of input conditions.
Program the end fence unconditionally.
Do not next MCR zones with other MCR or ZCL zones.
Each zone must be separate and complete.
Introduction
Output Override Instructions