RSLogix 5000 BOOL Base tag not activating output

[Kris Salmons 0]

I have a Base tag of BOOL logic that will not activate the MOV output.  The Base tag is paralleled with an Alias tag for a NO pushbutton.  When the pushbutton is actuated it produces the desired output.  Has anyone encountered this issue from a togglebit base tag before?  Why would a base tag produce a different outcome from that of an alias tag that function properly?

[panic mode 246]

1. is the logic scanned?  

2. if it is scanned, is there anything else that may change the value back? if things happen quickly, you won't see them.... you can add another flag or counter parallel to MOV to detect if this is the case

 

[ElectronGuru 81]

In addition to what panic mode has suggested, right click on the output tag and cross reference it. This will show you everywhere in the code that tag is use. You're looking for another output instruction with that tag that is scanning that it back to a false condition after you think it should be on. 

Make sure you check panic's first suggestion before you do anything else. Verifyt the controller is in the run mode, the routine that contains the instruction is being called, the instruction is not between a set of MCR instructions, etc. These are all simple "gotcha's" that will have you chasing your tail in circles if you don't catch them early.

[panic mode 246]

yup. cross reference is an excellent idea and making sure if is a correct variable and not one with same name but different scope.

[ElectronGuru 81]

DOH! Program vs controller scoped tags. Yet another gotcha! Good call panic!

[Kris Salmons 0]

Thank you all so much for the helpful suggestions!

So far, we have verified the subroutine instruction is not controlled by MCR or other latching logic.  There are no cross-references or duplicated tags for the base tag or the MOV instruction's destination.  We double-checked the base tag's scope but I had not considered the MOV function's destination tag scope.  Tomorrow (7-17) is our next opportunity to troubleshoot the problem and we'll give it a shot.  Again, I appreciate the feedback!

[Izzybe 13]

yes cross reference tag and see where it is being used. Also, sometimes I put an additional catch in there (a test tag that is a latch in front of the mov command). I know then for sure that the MOV command was executed. If the latch is not latched, that means you are working on fumes and you forgot to call out the subroutine in the main program. 

 

 

[Armadillo852 25]

On 7/16/2020 at 1:54 PM, Kris Salmons said:

Thank you all so much for the helpful suggestions!

So far, we have verified the subroutine instruction is not controlled by MCR or other latching logic.  There are no cross-references or duplicated tags for the base tag or the MOV instruction's destination.  We double-checked the base tag's scope but I had not considered the MOV function's destination tag scope.  Tomorrow (7-17) is our next opportunity to troubleshoot the problem and we'll give it a shot.  Again, I appreciate the feedback!

Am I missing something here? You say the base tag has no cross-references or duplicate tags. How is this bit being controlled? Are you just toggling this bit in the PLC? What exactly is turning this bit on?

[Kris Salmons 0]

The base tag is controlled by an HMI button. Using "Toggle" in RSLogix produces the same results as actuating the HMI button.