RE: PCI PCB Specification

[Jim Sather <jsather@sbs.com>]

Figure 5-19: 32-bit Connector, clearly details a notch on the right side
which, when present, allows insertion of a 64-bit card in a 32-bit
connector. Unfortunately, the purpose of the notch was nowhere explicitly
stated, and 64-bit cards were vaporware for years. Also for years, several
manufacturers have made 32-bit connectors without the little notch, a fact
I, for one, didn't notice before 64-bit PCI cards actually were
manufactured.

In this case, the PCI specification was too subtle for me, not to mention
the connector manufacturers who didn't follow the drawing in exact detail. 

Too late! Now we all know you have to watch for the little notch when
specifying 32-bit connectors or purchasing motherboards or backplanes with
32-bit connectors. Real world problem: those manufacturers may still be
tooled up for the bum connectors. It may take a while for them to disappear.
After all, how many end users are plugging 64-bit cards into 32-bit
connectors?

Jim Sather
SBS Technologies, Inc.

-----Original Message-----
From: Richard Walter [mailto:rwalter@Brocade.COM]
Sent: Wednesday, August 02, 2000 3:41 PM
To: 'pci-sig@znyx.com'
Subject: Re: PCI PCB Specification


Folks,

PCI 2.2, section 5.1, paragraph 2, sentence 4:  "In one orientation, the
connector is keyed to accept 5V system signaling environment boards; turned
180 degrees, the key is located to accept 3.3V system signaling environment
boards."

So:
a) The statement that "5V & 3.3V are identical ... except for the width of
the plasic at the ends" is wrong.  The width of the plastic at the ends is
the same.  32-bit 3.3V & 32-bit 5V connectors are, by definition, identical,
except for orientation only.

and

b) If there are 32-bit connectors in existence which don't allow 64-bit
cards to fit due to excess plastic at the end, then that is a fault of the
connector company to make connectors to the correct specification, not
the fault of a motherboard manufacturer trying to erroneously substitute
32-bit 3.3V parts for 32-bit 5V parts.

> From: Neal Palmer [mailto:neal@dinigroup.com]
>
> We have seen the same problem with motherboards.  Apparently somebody had
> an overstock of 3.3V PCI connectors and dropped the price significantly,
> and it turns out that the 5V connector and the 3.3V connector (32-bit
> versions) are identical except for the marking for pin1, and the width of
> the plastic at the ends of the socket.
>
> So a bunch of motherboard manufacturers decided to save $0.01 and use
> the 3.3V connectors soldered on backwards.  It's just too bad for all of
> those customers who didn't know what they were buying...
>
> -- Neal

Sincerely,
-Richard Walter
rwalter@brocade.com
Note: I speak for myself, not for Brocade Communications.