RE: RE: 3.3 Volts and PMC Modules

[Ivor Bowden <ivor@peritek.com>]

You are right. I wonder what percentage of new PMC boards
rely on the 3.3V being there (and what are the consequences
if inadvertantly plugged into a slot that does not provide),
and what percentage of new and existing slots provide do 3.3V?

Anyone making PMC boards that rely on 3.3V? What would happen
to them if only 5V were applied (latchup problems, etc)?

Anyone making PMC slots (CPUs, etc) that do NOT supply 3.3V?
If so, why?

Ivor

At 06:02 PM 3/22/00 -0800, you wrote:
>Actually, I think the PMC spec is independent of the PCI spec revision.  IE,
>it doesn't _require_ any particular rev of the PCI spec; rather, it requires
>that the PMC and baseboard equipment vendors document what version of PCI
>spec they meet and whether or not 3.3v is required/supplied.  I would hazard
>to say that the vast majority of new baseboard PMC equipment will supply
>3.3v.  
>-- BrooksL
>
>..snip..
>> So even though PCIv2.2 requires 3.3V, the current PMC
>> specification only requires PCIv2.0 compliance, and
>> does not require 3.3V to be present.
>> 
>> I have seen CPU boards with PMC slots without 3.3V.
>> 
>> We still put 3.3V regulators on our PMC boards.
>> 
>> imho, not requiring 3.3V on PMC slots from the beginning
>> was NOT a good idea. The small PMC cards can already have
>> enough heat dissipation problems without having to dump
>> heat from regulators, not to mention the wasted space.
>> But, can not change the past, PMC boards need 3.3V
>> regulators if they are to work in arbitrary PMC slots.
>> 
>> Ivor
>> 
>> At 02:50 PM 3/22/00 -0800, you wrote:
>> >I quickly scanned the PMC spec (IEEE P1386.1) draft 2.0 and 
>> found only that
>> >the electrical and logical layers are defined by the PCI 
>> spec (revision
>> >independent).  The PMC spec was written when PCI 2.0 was 
>> current and which
>> >does not require 3.3v on a 5v slot.  However, PCI 2.2 is now 
>> the current
>> >revision and that does require 3.3v on all PCI slots.  
>> Regardless, in the
>> >PMC spec, under section 4.1 'Conformance', it states "the 
>> vendor claiming
>> >compliance shall specify in the product specifications, 
>> those areas of
>> >compliance where optional features are allowed."  PCI spec 
>> revision and/or
>> >availability of 3.3v, falls under this product documentation 
>> requirement.
>> >-- BrooksL
>> >
>> >> -----Original Message-----
>> >> From: Louis Przebienda [mailto:lprzebienda@acromag.com]
>> >> Sent: Wednesday, 22 March, 2000 12:42
>> >> To: pci-sig@znyx.com
>> >> Subject: 3.3 Volts and PMC Modules
>> >> 
>> >> 
>> >> Hello All,
>> >> 
>> >> Do PMC modules provide their own 3.3 volts onboard via an 
>> >> onboard regulator,
>> >> or do they rely upon the cards they plug into to provide 3.3 volts?
>> >> 
>> >> For those who have designed PMC modules, what did you do?
>> >> 
>> >> For those that have designed cards with PMC module slots, do 
>> >> you provide 3.3
>> >> volts to the PMC module slots?
>> >> 
>> >> The Electrical Specification for Common Mezzanine Card 
>> >> P1386/Draft2.1 dated
>> >> 11-Oct-99 in paragraph 6.1 states :"The CMC standard allows 
>> >> +5V, +3.3V and
>> >> +/-12V.  Which of these voltages shall be provided is 
>> defined in the
>> >> specific bus standard:".  The bus standard is the PCI bus 
>> >> spec.  As we know
>> >> PCI 2.1 spec did not require the 3.3V power pins to be driven. 
>> >> 
>> >> I would be grateful for any comments, experiences or 
>> insight into this
>> >> matter.
>> >> 
>> >> Thank you for you assistance.
>> >> 
>> >> Louis Przebienda
>> >> Designs Engineer
>> >> Acromag Inc.
>> >> Email: lprzebienda@acromag.com
>> >> 
>> >> 
>> >
>> >
>> >
>> 
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