Rockwell Automation 1772-LV Mini-PLC - 2/15 Programmable Controller (Series B) Programming and Operations - Manual (Page 180)

Quick Reference Section
Appendix A
AĆ11
Table A.H
Program Control Instructions
NOTE: The MCR and ZCL boundary instructions have no word address.
The word addresses, XXX, of the immediate input and output instructions are limited to the input and output image tables
respectively.
Displayed word addresses will be 23 or 4 digits long, depending on data table size. When entering the word address, use a
leading zero if necessary.
Key Symbol Instruction Name
1770-T3
Display Explanation and Rung Conditions
-(MCR)- Master Control Reset -(MCR)- Two MCR instructions are required to control a group of
outputs. The first MCR instruction is programmed with input
conditions to begin the zone. THe second MCR instruction is
programmed unconditionally to end the zone.
When the MCR rung is true, each rung condition controls their
output instruction.
When the first MCR rung is false, all non-retentive bits in the
zone are reset.
WARNING: Do not overlap MCR zones, or nest with ZCL
zones. Do not jump to a label in MCR zones.
-(ZCL)- Zone Control Last State -(ZCL)- Two ZCL instructions are required to control a group of
outputs. The first ZCL instruction is programmed with input
conditions to begin the zone. The second ZCL instruction is
programmed unconditionally to end the zone.
When the ZCL rung is ture, all output instructions within the
zone act according to the logic conditions preceding them.
When the first ZCL rung is false, outputs in the zone will
remain in their last state.
WARNING: Do not overlap ZCL zones, or nest with MCR
zones. Do not jump to a label in ZCL zones.
-[I]- Immediate Input XXX
[I]
Processor interrupts proram scan to update input image table
with data from the corresponding module group. It is updated
before the n ormal I/O scan and executed each program scan.
-( IOT )- Immediate Output XXX
-( IOT )-
When rung is true, the processor interupts program scan to
update a module group with data from its corresponding output
image table word address. It is updated before the normal IO
scan and executed each program scan when the rung is true.
Can be programmed unconditionally.