ON CHANGE command

Forgive me if this has been asked and answered. I searched through the archives but could not find anything relevant.

I am programming in RSLogix 5000 and wish to perform an action when a STRING tag changes. The only only way I know how is to compare the new value to a different tag that has the old value, then move the new value into the old value tag.

This is very inelegant. Is there an "on change" command?

Thanks,
Tom

Not that I know of. I always use the compare method as you stated. You could probably roll you own with some type of add on instruction.

If you think about it, any ONCHANGE command for strings would have to do precisely the same thing you are doing. Far from inelegant it seems like the simplest way of achieving your goal.

If you weren't use a STRING then the DTR instruction would do the trick, but it is not valid on STRING tags. I think most use the compare method instead.

OG