[obieron]

True or not true? A bit new to FANUC ladder but not to AB and such. Why does an output highlight and turn on even though it's rung functions are not highlighted? Troubleshooting is crazy like this! Why does FANUC do this? I'm on an 18-T . . . can anyone throw me a bone?

[psevin]

The only time I've ever seen this on a Fanuc control is when the output is written to in two different rungs.

[Al_The_Man]

Also occasionally it will happen if the rung is made except for one bit, if this one bit is changing fast it does not update on the screen but completes the rung the majority of time.
As paul says, check for duplicate use of output, not very good practice however.
For e.g. I have seen an output written in an Auto section and a manual section, and only one section is enabled at a time but the output will still show on in both.
Al.

[bob1371]

Also look for the little tick mark in the rung \ this will invert the output logic.

Bob

[psevin]

Another possible cause may be a jump function prior to the logic. Any logic placed between the jump & jump end functions won't be executed to completion when the jump function (SUB 10?) is enabled.