Is there an easy way to tell what operating mode a PLC is in? I was hoping there is a register that gives that status similar to what AB does.

What PLC is it?

Actually I would like to do this with multiple CJs and CSs. The one on my desk is a CJ1H-CPU65H.

Do not have CJ1 to try, but in CP1 any non-holding coil driven by P_On (Always On) contact does the job.

You might find this post useful: http://forums.mrplc.com/index.php?s=&s...ost&p=85280