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While the rung state of the first MCR instruction is true, execution
proceeds as if the zone were not present. When the rung state of the first
MCR instruction is false, the ladder logic within the MCR zone is executed
as if the rung is false. All non-retentive outputs within the MCR zone are
reset.
MCR zones let you enable or inhibit segments of your program, such as
for recipe applications.
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.
TIP
ATTENTION
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.
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.
Program Control Instructions
Publication 1763-RM001C-EN-P - October 2009
253
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