The MCR instruction is used as a soft emergency stop. Rungs placed between two MCR instructions can be disabled; or rather the outputs of the rungs are disabled when the MCR instruction is false and enabled when true.
There are a couple of rules to follow:
- Don’t jump into an MCR zone as unexpected action will occur.
- The zone must end with an unconditional MCR instruction usually (see last rule).
- Don’t nest one MCR zone within another MCR zone.
- If an MCR zone continues to the end of a routine it is not necessary to end the zone with an MCR instruction.
Note: The MCR is not a valid substitution for a hard-wired emergency stop circuit or master control relay. Use a hard-wired master control relay for emergency stop power shutdown.