FSC Instruction to check bits

MQuintan · Jan 21, 2013

Hello:

I have an application where a "first-out" indication is sent to bits starting at N36:0/0 and ending at N36:15/15. Thre are 192 bits that I need to check, only one will be true when this "first-out" happens.

My question is: can I use an FSC instruction to check which bit (from 1 to 192) is the one which is true? It is not clear to me if this can be done?

Ron Beaufort · Jan 21, 2013

take a look at the FBC (File Bit Compare) instruction instead ... if I understand what you're asking for, I think you'll find that one more suitable ...

and welcome to the forum ...

MQuintan · Jan 21, 2013

Thanks! I think that will do the trick!

Ron Beaufort · Jan 21, 2013

by the way, is your "first out" signal coming from a series of digital input modules? ... if so, there's a "secret handshake" that you might be interested in that could affect the accuracy of your results ... a lot depends on how you're wiring up the inputs ...

let us know if you need more detail ...

MQuintan · Jan 22, 2013

No, actually it's sent from another PLC's logic.

Ron Beaufort · Jan 22, 2013

No, actually it's sent from another PLC's logic.

in that case you PROBABLY don't have anything to worry about ... the effect that I had in mind is covered in a thread from 2007 ... the major idea is summed up in the following post ...

http://www.plctalk.net/qanda/showthread.php?p=246883&postcount=25

it all boils down to the fact that many of the "first out" schemes that people come up with are not as reliable as they might want to believe ...

party on ...

MQuintan · Jan 22, 2013

Thanks, Ron. I read the post.. Very interesting. However, this does not apply to my situation now, but it is definitely something to keep in mind.

Cheers!

FSC Instruction to check bits

MQuintan

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