micrologix...JMP and LBL

[Skidood]

Hello again, Happy New Year.
If the bit controlling this subroutine switches off, causing the JMP and LBL instructions to take effect, will the valve stay on?
Thanks !!

 

[plvlce]

Assuming B3:17/2 is not written to elsewhere it will stay on, unless/until the PLC leaves and re-enters run (eg due to a power cycle) with the subroutine switched off.

In that scenario the prescan will turn off the bit, and it will never be scanned to turn it on again until the subroutine is enabled.

In the scenario where the subroutine is enabled but then disabled while running, you are correct that it should stay on.

 

[Skidood]

Assuming B3:17/2 is not written to elsewhere it will stay on, unless/until the PLC leaves and re-enters run (eg due to a power cycle) with the subroutine switched off.

In that scenario the prescan will turn off the bit, and it will never be scanned to turn it on again until the subroutine is enabled.

In the scenario where the subroutine is enabled but then disabled while running, you are correct that it should stay on.

Thanks. Makes sense as the rung with the valve will not be evaluated so there is nothing to turn the valve bit OFF.

 

[padees]

If you want to keep the program the way it is, you can use an OTU to turn the bit off when the subroutine isn't being called, but that instance would need to be in a scanned routine. It's a bit messy doing that.