Momentum Status


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I'm trying to find a "watchdog" register to use to determine when this processor is in "run" mode. According to the manual the STATUS block should do this. but it doesn't change the "RUN Light" indicator bit when the processor isn't running, presumably because the block isn't being scanned and so doesn't update the registers.

I can't find a "Last scan before shutdown bit" with which I was hoping to zero a register.

Does anyone know how this can be achieved?

I DON'T want to read a counter register twice over time and compare the two readings, as I don't have that facility in the monitoring software, just bits and registers.

You did not say if you are using a Unity Momentum or Non-Unity Momentum. The "run" bit in non unity controllers is, unfortunately, a "system bit" that the developers exposed to the world. It actually means nothing to a PLC programmer. Unity processors have far more system bits and words but using the "run" is still not a good idea.

Simple method, turn a bit on/off in the momentum, say every 2 seconds.
Program a free running timer in the "master" device that is reset by both the positive or negative transitions of this bit (to avoid cases where it remains on or off). It this timer is set for 5 seconds, you would have to miss a few transitions before the timer "times out" and gives you an alarm (that you can latch/reset). No need to read registers.

There are other methods such as monitoring communications status and errors.
Thanks for the reply, not Unity, ProWorx.

We don't have the ability to write to the PLC only reading, unfortunately, and we can't even do it in hardware as the I/O is used up!

Thanks for the help though.