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

[Ted Firlit <firlit@utmc.aeroflex.com>]

Ivor, 

Just to add to your comments, PCI Local Bus Spec para 4.1.1 describes the use of the VIO pins.  Universal boards should at least diode clamp their I/O buffers to the VIO pins, if they do not use the VIO voltage as a supply.


Ted 

Ivor Bowden wrote:
> 
> 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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-- 
Ted Firlit		      		(719) 594-8138
Senior Design Engineer
UTMC Microelectronics Systems
4350 Centennial Blvd., MS 1004
Colorado Springs, CO 80907