Rockwell Automation 1772-L8_LW_LWP_LX_LXP,D17726.5.8 User Manual - Manual (Page 138)

Chapter
10
10-1
Program Control Instructions
This chapter describes these program control instructions:
output override
immediate I/O update
Some applications 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 satisfy this need.
The output override, or zone type instructions, operate similarly to a
hardwired master control relay in that they affect a group of outputs in the
user program. But these instructions are not a substitute for a hardwired
master control relay, which provides emergency I/O power shutdown.
The following table illustrates specific instructions for these categories:
Output Override Immediate Update I/O
Master Control Reset Immediate Input Update
Zone Control Last State Immediate Output Update
Master Control Reset and Zone Control Last State
ATTENTION: Do not place a LABEL instruction in an MCR
or ZCL zone. When jumping over a start fence, the processor
will execute the program from the label to the end fence as if
the start fence had been true. The start fence may have been
false, so that all outputs within the zone are controlled by the
output override instruction (i.e. OFF for MCR or last state for
ZCL instructions).
Failure to observe this warning could cause unexpected
operation with possible damage to equipment and/or injury
to personnel.
Chapter Objectives
Introduction
Output Override Instructions