MCR Application

daba said:
That is incorrect Vince, the rungs of code within an MCR "zone" are still executed, but effectively with the "power-rail" turned OFF. That has the effect of turning off all non-retentive outputs, resetting all TON's, start TOF's timing, etc., etc.

If you really want to ignore sections of code, use JMP/LBL, that truly does ignore the jumped rungs.
Click to expand...

Ah, okay. Thanks for the advice, I will use that from now on.
 
The only time I've used this instruction was in school, when we had an assignment where we needed to use the instruction.

Some things they make you learn for the sake of learning, and respecting the past.
 
You have to learn it.. in case someone else actually uses it.

"The only defence against an MCR is knowing how it works."

If AB cared about the MCR, they would invest a few programming hours making the power bar change colour when it is in operation.
 
I believe they do, in the new versions.

At least, if the subroutine is not called from anywhere, the power rail is no longer green. Never come across an MCR in the wild to know if it applies there too :)
 
A long time ago in a one horse town not far enough away, there was a PLC with 4k of memory running a very complicated assembly machine that needed the MCR to save every nybble it could spare...

I agree with all the previous comments...especially this one:

If AB cared about the MCR, they would invest a few programming hours making the power bar change colour when it is in operation.
Click to expand...
 
MCR Sample

MC and MCR are used to reset larger sections of logic. I have seen this used extensively to reset latching rungs. This is a pseudo state machine which maintains the state of a channel . If the machine stops and a the channel is checked the stop point and related input contacts are quickly identified.


-------||------------------------[MC]

       Start

------||---------------------------()

Condition1     |                    Out1

               |

-----||------ 

  Out1 



------||--------||--------------------------()

Condition2   Out1     |                     Out2

                      |

-----||-----------------

  Out2



------||--------||--------------------------()

Condition3   Out2     |                     Out3

                      |

-----||-----------------

  Out3



---------------------------------[MCR]

 
Last edited:

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