Always on/off bits

[TimWilborne 108]

My SWAG is it had something to do with the 8 character limitation originally. Think those early PLCs had 5 digits for the address so that would leave 3 for the instruction preceding it. If any of that is true guess they keep it for compatibly. Hey Sleepy - Did you know that RsLogix 5000's function blocks have moved on to 4 letter words

[Clay B. 1]

Now this was a long time ago, I was actually using a VPU to give you a time reference about the size of a suitcase. What went for portable back then.... Anyway, I asked the same question and was told the reason it is XIO and XIC is that it stood for Examine if On and Examine if Off. Never understood how Off became C. The reason it is this way is that it is not truly a normally closed contact, what your actually looking for is that input to be off. They wanted to make sure Electricians did not confuse and Examine OFF with a Normally Closed contact. As for AFI that was always an agreed apon name for a disabling bit. Infact I still do searches on AFI when looking at a new program. The more you find the more you know the program has been altered from orginal. I have no idea who came up with it but I have seen it in programs all over the place. My guess would be someone from AB came up with the idea and it was taught in one of their training classes. Heck I remeber on an TI VPU they had keys labled XIO and XIC.

[TConnolly 13]

Oh, is that what it stands for? ;) I always thought it was the All F*****up Instruction, mainly because its used when something is AFU.

[newpageboba 7]

XIC is Examine Input Closed XIO is Examine Input Open

[Mickey 71]

Wrong: XIC_XIO.pdf

[Sleepy Wombat 27]

I know a lot of 4 letter words that I will not bear utterance on this forum..