XIC confusion

I know this is an elementary question for most. Please reply, even if you feel it is beneath you. I have been in relay logic land for many years, and am still learning how to think PLC logic. So thanks in advance for your help
XIO or Examine off. Display is a set of normally closed contact. In ladder logic, when is this instruction actually true? I understand the XIC with no problem, but in reviewing an RTO timer with an XIO, I think I have it backwards. I know it is simple, but simple is hard for me sometimes.
Thanks again for the answer!

"'XIO', when is this instruction actually true?"

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It "solves true" (passes power) when its value in the data table is a 0.

Don't worry about XIO or XIC - they are Allen Bradley specific terms. The symbol that shows is accurate, and may be treated like the corresponding relay contacts. XIC or -] [- is simply a normally open contact that closes if the associated input or coil is true or turned on. XIO or -]/[- is simply a normally closed contact that opens when the associated input or internal coil is turned on.

fmichael said...

XIO or Examine off. Display is a set of normally closed contact. In ladder logic, when is this instruction actually true?

I'm gonna be a little picky here... but then, it might provide just the right amount of light.

You said... "...when is this instruction actually true?"

OK... picky... The "instruction" is never TRUE... nor FALSE for that matter.
The "instruction" calls for the examination.
The "symbol" determines the type of examination performed.
The RESULT of the examination will be TRUE or FALSE.
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--| |-- says... See if the signal is ON.

If the signal is ON then the RESULT is TRUE.

If the signal is OFF then the RESULT is FALSE.
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--|/|-- says... See if the signal is OFF.

If the signal is ON then the RESULT is FALSE.

If the signal is OFF then the RESULT is TRUE.

beerchug Thanks for all the replies. bonkhead