RE: 3.3 Volts and PMC Modules

[Ivor Bowden <ivor@peritek.com>]

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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