23 Jan
2001
23 Jan
'01
11:06 a.m.
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(a)p850ug1.demon.co.uk>
To: <classiccmp(a)classiccmp.org>
Sent: Tuesday, January 23, 2001 2:16 PM
Subject: DD50 SCSI connector
times.
>
> 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
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