Easy, now, Tony ... I "feel your pain" (using the popular clintonism) about
the notion of standards with respect to folks working mainly with PC's, but
you must remember that the SUN-style DD50 for SCSI is not in the SCSI
standard. It's probably a better connector than the telco-style connector
that is, but it's so much more expensive (the same $30 that the IDC version
really does cost would buy two or three of the SCSI-1 cables at the local PC
store) that nobody really worries about it much.
BTW, DEC was the one that corrupted the notion of "standard" usage of the
connectors on serial I/O cabling. They were at one point the most
standardized users of the DB-25, with 'S' connectors on the bulkead and 'P'
types on the cables, but then they wandered away from their own usage
conventions. Once upon a time you could tell whether the cable was for DTE,
DCE, or was a null modem, just by looking for pin 20. If it was populated,
that end went to the terminal equipmen. If pin 6 was populated, it went to
DCE. If it had one at each end, it was a null modem cable. <sigh> Those
were the "good old days."
Dick
----- Original Message -----
From: "Tony Duell" <ard_at_p850ug1.demon.co.uk>
To: <classiccmp_at_classiccmp.org>
Sent: Tuesday, January 23, 2001 2:16 PM
Subject: DD50 SCSI connector
> >
> > On 23 Jan 2001, Iggy Drougge wrote:
> > > What kind of connector is it? How many pins, what does it measure? The
SUN
> > > SCSI boxes I've encountered have either used Mini-DB50 (modern ones)
or
> > > Centronics-50 (big old ones).
> >
> > They're the large three row 50 pin D type (not centronics). Somebody
told
> > me off list that they were the standard type on Sun 3 machines.
>
> Sounds like a standard DD50 connector. It is one of the standard SCSI-1
> connectors, used on all sorts of machines (Suns, PERQ 3as, etc).
>
> One thing worth knowing about this connector is that if you take the IDC
> version of the plug or socket and crimp it to a piece of 50 way ribbon
> cable, the signals are in the same order as those on a piece of ribbon
> cable crimped to the 50 pin Amphenol (often incorrectly called
> 'Centronics') connector or crimped to a 50 pin 2 row header socket to fit
> the plug on a disk drive. So it's easy to make up adapters between the
> DD50 connector and the Amphenol one (say) -- just crimp the connectors
> onto a short piece of 50 way IDC ribbon cable, taking care to get pin 1
> of each connector at the same end of the cable. I've done that several
times.
>
> The problem with this is that the DD50 IDC connectors are quite
> complicated to make and thus expensive. Expect to pay \pounds 20.00 (say
> $30) each for them.
>
> It would appear that any connector not commonly used on PCs can't be a
> 'standard' to most people. I've got fed up with explaining to the goons
> in the local PC shops that a standard serial port has 25 pins on a DB25
> connector and that the DE9 serial port on PC/AT and later machines is not
> a true standard. Oh well...
>
>
> -tony
>
>
Received on Tue Jan 23 2001 - 16:06:34 GMT