Rockwell Automation 1761-HHP-B30 MicroLogix 1000 with Hand-Held Programmer (HHP) - Manual (Page 222)

Chapter 12
Using Program Flow Control Instructions
12–6
Use MCR instructions in pairs to create program zones that turn off all the
non-retentive outputs in the zone. Rungs within the MCR zone are still
scanned, but scan time is reduced due to the false state of non-retentive
outputs. Non-retentive outputs are reset when their rung goes false.
If the MCR Rung that Starts the Zone is: Then the Controller:
True Executes the rungs in the MCR zone based on
each rung’s individual input condition (as if the
zone did not exist).
False Resets all non-retentive output instructions in the
MCR zone regardless of each rung’s individual
input conditions.
MCR zones let you enable or inhibit segments of your program, such as for
recipe applications.
Entering the Instruction
You enter the instruction from within the program monitor functional area.
P 0 0 9 M C R
When you program MCR instructions, note that:
•
You must end the zone with an unconditional MCR instruction.
•
You cannot nest one MCR zone within another.
•
Do not jump into an MCR zone. If the zone is false, jumping into it
activates the zone.
Important: The MCR instruction is not a substitute for a hard-wired master
control relay that provides emergency stop capability. You still
must install a hard-wired master control relay to provide
emergency I/O power shutdown.
!
ATTENTION: If you start instructions such as timers or
counters in an MCR zone, instruction operation ceases when the
zone is disabled. Re-program critical operations outside the zone
if necessary.
(MCR)
Execution Times (
µ
sec) when:
True False
3.98 4.07
Ladder representation:
Master Control Reset (MCR)
5 3
U
ENT
1
FUN
To enter the function code, press: