RE: RE: 3.3 Volts and PMC Modules

[Hugh Tarver <hwt@transtech-dsp.com>]

Our PMC modules have 3.3V regulators (just in case).  However, the draft 
2.0 PMC specification states in the pin section 5.2: ' PCI Mezzanine cards 
and hosts that support PMC slots shall assign the local bus signal pins per 
the pin assignment given in Table 5-1.'   Table 5-1 includes the +3.3V 
lines without any caveat regarding optional use for motherboards.  For this 
reason our PMC carrier cards supply 3.3V to every PMC slot.
The only PMC carriers which I have come across without 3.3V supplied have 
been PCI-PMC passive adapters which have carried the 3.3V from the PCI 
connector to the PMC slot.  In most PCs the 3.3V isn't there from the PCI 
slot, so it isn't available to the PMC slot either.  We overcame that by 
designing our own motherboard including a 3.3v regulator.

Hugh

Hugh W. Tarver
Transtech DSP
Manor Courtyard,
Hughenden Avenue,
High Wycombe,
Bucks.
England.
HP13 5RE

On 23 March 2000 18:43, Ivor Bowden [SMTP:ivor@peritek.com] wrote:
> 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
> >> >>
> >> >>
> >> >
> >> >
> >> >
> >>
> >
> >
> >
>