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Re: CPCI: Question on Definition of V(I/O) pin



If you are talking about plug in cards, then
if your board is keyed for 3.3V ONLY
you may connect the VIO pins to 3.3V, and
if your board is keyed for 5V ONLY
you may connect the VIO pins to 5V, and
If your board is keyed for universal (no key)
you may NOT connect the VIO pins to either 3.3V or 5V.
However, if your board is not universal you will be SAFER
to just bypass the VIO pins and not connect them at all.
If this is contrary to any part of the CPCI spec, I would
appreciate anyone telling me what section covers that.

If you are talking about backplanes
VIO must be connected to either 3.3V or 5V
(there is no universal back plane).

-Ivor

At 01:39 PM 3/21/2002 -0500, you wrote:
>Hi All,
>
>In reading through the cPCI specification, I am somewhat confused as 
>to the true definitive use of V(I/O) pins. Are they ONLY to be used 
>by boards that can operate from EITHER 5V or 3.3V, meaning that all 
>other boards would only tie to the appropriate 5V OR 3.3V as they 
>require? OR, can any board tap into these assuming they are wired to 
>the correct voltage for that system? Meaning if every board in my 
>system has 3.3V cPCI signalling, I would tie V(I/O) to 3.3V, and 
>everyone could use those pins in addition to the "regular" 3.3V pins?
>
>Basically, what are the proper uses of these pins, and if not needed, 
>should I just stick with either the 5V or 3.3V defined pins to power 
>boards?
>
>Thanks
>
>Amy Hurley
>-- 
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>Amy J. Hurley
>Naval Research Lab - Code 8132
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