Latching bit

I have a program that was emailed by OEM out of Italy for adding a new conveyro to an existing line and 2 Photo eyes. the problem I am having is ther is a latch bit that continues to unlatch itself even after removing all unlatch bits from the program. I can go into the data table and change the bit from low to high but as soon as I switch from program to run it unlatches itself. Nothing that is done can seem to prevent this from happening. If I wasn't seeing this happen right in front of me I would say that someone is pulling my leg. I am running the newest version of RS Logix on a SLC 5/04 processor. With a Panelview Plus 1000 touch screen using RS View Machine Edition Studio version 4.0.

Anyone have any ideas as to why this happening?

Dowpin

It sounds like the OTL address is being written to by another part of the program or HMI. I would search for all usage in the program and HMI.

If you can post your code I am sure someone will look at it and try to help.

Try it with the HMI disconnected.

A button that is a toggle instead of a momentary will do this. A way to prevent it is to always use the logic to reset the command bits, even if the HMI is supposed to be doing it.

Them HMI's ain't as smart as they like to think they are...

And just to add one more thing to the list...

The code you are looking at has a JSR calling it, yes?

Another thing to check is if the word where the bit is located is being "cleared" in the program. For example if the latch bit is N7:0/0 and somewhere in the program there is a MOV command moving zero into N7:0. Try searching for the word to rule this out.

could be an "unused" OTE lurking in the underbrush ...

basic idea: if there is an OTE (Output Energize) instruction ANYWHERE (I repeat ANYWHERE) in the program, then the bit address will be UNlatched whenever the processor first goes into the Run mode ...

so be sure to check for an OTE for the same bit - even/especially in any UNUSED subroutines ... believe it or not, the processor will PRE-scan ALL (I repeat ALL!) subroutines (even left-over "junk" ladder files that are no longer "called" by JSR instructions) just once at start-up/go-to-run ... even if the unused/uncalled rung happens to be TRUE, the OTE will still be executed with false logic during PRE-scan ... this will UNlatch the rung just like an OTU instruction ...

if this turns out to be your problem, you might want to read this post for more detail on this same subject ...

and I'll go along with the others who have suggested that you post your program ...

latching bit?

Thanks, found in HMI programming.

glad you found it ... thanks for coming back and letting us know ...

and welcome to the forum ...