50 pin SCSI to 50 pin centronics

From: Richard Erlacher <edick_at_idcomm.com>
Date: Thu Apr 12 09:39:56 2001

In an earlier discussion of the RS232 connectors used in various systems it was
pointed out that DEC used the DE9 before anybody thought of the PC/AT.
Considering the common usage of so few of the defined signals on the DB25 and
the rarity of the cases wherein more than half-a dozen of the signals are
needed, I think it's reasonable for a system that uses lots of serial ports to
use a small connector.

However, as scantily documented as the signal set in the 9-pin connector has
been, I think it was a poor choice for the PC/AT. You can bet, however, that
someone got a big raise for thinking up a way to get two ports out through a
backpanel where only one might otherwise have fit, just as someone probably did
for thinking up that "twisted cable" scheme for PC floppy and hard disks.

Dick

----- Original Message -----
From: "Iggy Drougge" <optimus_at_canit.se>
To: <classiccmp_at_classiccmp.org>
Sent: Thursday, April 12, 2001 6:15 AM
Subject: Re: 50 pin SCSI to 50 pin centronics


> On Wed, 11 Apr 2001, Tony Duell wrote:
>
> > IIRC, the RS232 standard specifies a 25 pin connector. So strictly there
> > are no 9 pin RS232 ports. If you mean why do PC/AT machines have a DE9P
> > for the serial port, it was because (a) 9 pins is enough for the active
> > signals on said port and (b) you can fit a DE and a DB on a single PC
> > bracket, so you could have a combined parallel/serial adapter card. Which
> > IBM introduced with the PC/AT IIRC.
>
> Oh, but then you lose a lot of fun. The Amiga DB25 serial port features
> among others audio output on some pins. =)
>
> > And Apple used the 8 pin mini-DIN on the Mac+ and later because there
> > wasn't room for the DE9 connector used on the earler Macs. Hardware
> > hackers have been complaining ever since -- those mini-DINs are about the
> > worst connectors in the world to wire!
>
> Try a DIN-13 for size.
>
>
Received on Thu Apr 12 2001 - 09:39:56 BST