12 Apr
2001
12 Apr
'01
10:39 a.m.
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(a)canit.se>
To: <classiccmp(a)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.