Reset whole bit-word AB Micrologix

[Dcook87]

I'm starting to learn some basic ladder logic. I'm on an AB Micrologix 1000 PLC.

I'm wondering if the OTU instruction will work on an entire bit-word rather than a single bit.

i.e.:

Will "OTU B3:2" reset all bits (0-15) in word B3:2 to 0, or would I have to go through and do an "OTU B3:2/0, OTU B3:2/1..." for all the bits I want to reset?


I would just try this out, but I don't have access to a PLC at the moment.

 

[bernie_carlton]

Use CLR B3:2 or MOV 0 B3:2

 

[Dcook87]

Use CLR B3:2 or MOV 0 B3:2

This doesn't seem to work for outputs. If my output circuit is de-energized (with an e-stop), will the plc "remember" these output states when that output circuit is re-energized? (assuming the PLC processor itself has not lost power..

If they don't get reset, is there any easy way to reset all outputs to 0?

 

[bernie_carlton]

Outputs, like any other position, only reacts to the logic driving it. If logic turns it on then it will stay on. In the Micrologix, like many other PLCs, the status of the output bit (unless 'forcing' is in effect) is applied to the actual output hardware after the end of the scan. So if there is logic which would turn off the output bit but it is followed in the scan by logic which would turn on the output bit the it will be on. This is colloquially called 'the last one wins'.

An E-Stop circuit will not usually 'de-energize' the output but will remove power from the output circuit so that it has nothing to switch to the load. This does not automatically instruct the internal logic to also turn off the output bit.

View this series of introductory lessons on PLC operation. Then come back with more questions.

If you wish, zip and post your current program for comments.