Troubleshooting by stepping through logic rung by rung in Control Logix

Don't know of an actual "Step" function built-in. However, when I have a difficult or dangerous series of logic (think complex servo motions), I use a "Debug" contact on each rung of logic. They are typically named something like DEBUG001, DEBUG002, DEBUG003, Etc. These contacts have NO LOGIC driving them! When executing the logic, these rungs only run when I am online with Logix5000, and turn the DEBUGxxx bit on using the toggle bit command (Ctl-T, or Right-Click & select from menu). That way I can watch each step complete before allowing the next to activate.

---------------------------------------------------------
For Example:

DEBUG001                                  Step1
-----| |------ ..... Misc Logic ..... -----(  )-----

DEBUG002                                  Step2
-----| |------ ..... Misc Logic ..... -----(  )-----
-----------------------------------------------------------

Hope this helps!

/David/

Not that I know of as PLC logic is always supposed to be "scanning". However, you might find the Trend tool useful. You can "watch" a bunch of tags, capture them during the operation of the machine, and then play it back like a logic analyzer. Very useful to capturing quick things that are happening.

I have also put in "trap logic" that looks for specific conditions and sets a bit, etc., just to see if something weird is happening.

Good luck!

If you have access to their emulator SW it has a single scan mode. That is all I am familiar with.