SUMMARY: DB-50 type SCSI connector info

From: Jim Lick (
Date: Wed Apr 15 1992 - 15:13:54 CDT

A while back I posted an article asking for information on the Sun
DB-50 type SCSI connector. I wanted to build a cable to go from my
Sun 3/60 to the centronics type connector found on most other SCSI
boxes. From the information below, I was able to build the cable,
and it has been working fine for the last couple of weeks. I couldn't
find an IDC type DB-50 connector, so I got a regular DB-50 and crimped
pins on each of the 50 wires from the ribbon cable, then inserted them
into the shell in the proper order. On the other end of the ribbon
I just snapped on the IDC type Centronics connector.

The main difficulty here is that there are two systems of number pins
on the connectors. There is ribbon order, and there is the connector
order. For ribbon order, the cable is 'straight through', 1 to 1, 2
to 2, 3 to 3, ... 50 to 50. Line 1 is the one on with the red stripe
on it, and they count up sequentially to 50 on the other side of the
ribbon. Between ribbon order and connector order, pin 1 is common to
both, but other than that, connector order varies, depending on the
connector type. If the pins on the connector are not labeled, pin 1
will likely have a small arrow, or some other marker pointing at it.

Obviously, the easiest thing is to get ribbon cable and IDC type
connectors for each end, or just buy a premade cable. If you feel
adventurous, see below for the ribbon order of pins on the DB-50
connector. For the centronics, the ribbon order is:

1 3 5 7 ... 49
2 4 6 8 ... 50

While the connector order is:

1 2 3 4 ... 25
26 27 28 29 ... 50

Figure out what the ribbon order correspondence is between pins on
both connectors, and then wire it up. Cross your fingers and hope
it works. It would probably be advantageous to use crimp-type pins
instead of soldering. I made a couple of mistakes but was able to
pop the errant pins out and reinsert them easily. (I made a pin
remover by drilling a shallow hole into the narrow end of a
plastic chopstick. It turns out that it was just the right size
to fit between pins, and sturdy enough to do the job. Cheap too,
a dozen for 99 cents I recall.)

Many thanks to all those who responded.

                            Jim Lick
Work: University of California | Play: 6657 El Colegio #24
      Santa Barbara | Isla Vista, CA 93117-4280
      Dept. of Mechanical Engr. | (805) 968-0189 voice/msg
      2311 Engr II Building | "when you gonna make up your mind?
      (805) 893-4113 | when you gonna love you as much | as i do?" -Tori Amos


From: (Martin Hobson)

I generally buy these cables ready-made from

CS Electronics
1342 Bell Avenue
Tustin, CA 92680
(714) 259-9100

They have good prices and quick service.


From: Carl Mueller <>

That's not it. The connectors are wired such that the physical
arrangement of the pins corresponds to the nearest wire on the
ribbon cable. While I don't know what this works out to exactly,
it's definitely NOT pin #n - pin #n.

-Carl (



I don't quite understand what you meant by centronics style connector? Do
you mean ribbon cable? If that's what you meant, here's what you might need.
You could buy an Insulation Displacement Connector of DB-50(mail order ~$18)
and follow the descriptions below(that's what I did, and it works).


The pin numbering of the IDC DB-50 is as following

1 4 7 ...
 3 6 9 ...
2 5 8 ...

Those numbers are also the sequence of the ribbon cable.

With another numbering scheme (in particular, the one on the female
DB-50 on the Sun CPU board), i.e.

 1 2 3 4 ...
  18 19 20 ...
34 35 36 37 ...

the pin sequence for the ribbon cable is

 1 34 18 2 35 19 3

In both of the "diagrams" above, the wide part of the D connector is
on top, same was as on the Sun CPU board. These views are from the pin
side of the male connector, or the back side of the female connector
(as in the view from the inside of the Sun CPU).

So, to spell it out in one more (hopefully consistent way), you would
solder a ribbon cable to a DB-50 by connecting pin one of the ribbon
(usually a red stripe on a gray ribbon) to the upper left pin
(actually, the upper right as you look at the back of the male
connector). The second wire goes to the bottom, the first in a
sequence of 16 diagonal rows of three pins. The remaining wire, pin
50, goes on the bottom again.




From: cdl@mpl.UCSD.EDU (Carl Lowenstein)

I hope you are not really "wiring" a connector. Get some ribbon cable
and a 50-pin IDC crimp-on connector of each type, and squeeze them
together. The time and labor saving is immense, and compensates
for the greater cost of the raw materials. Also it's hard to make
small mistakes in the wiring. :-)


From: (Andreas Schulz)

You find the description in the 3/60 Hardware Install Manual on
Page 42 Table B-5 :-), or even much better in a 3/50 Manual :

2 DB0
4 DB1
6 DB2
8 DB3
10 DB4
12 DB5
14 DB6
16 DB7
18 DBP (Parity)
20,22,24 GND
26 Best is to leave open, should be open at the sun, but they
        have some build wrong, SCSI it is the termpower ( +5V )
28,30 GND
32 ATN
34 GND
36 BSY
38 ACK
40 RST
42 MSG
44 SEL
46 C/D
48 REQ
50 I/O
all odd numbered Pins ( 1, 3, 5, ... ) are GND pins.

And the connector:

49 46 .......... 10 7 4 1
   48 ........... 9 6 3
50 47 .......... 11 8 5 2

Hope, this helps :-)


From: eirik@TC.Cornell.EDU

This is true only for one numbering scheme.

I don't know about the Centronics connector, but I suspect an IDC
(insulation displacement connector) on each end of a ribbon cable
would do what you want. I know that works with the usual header
connectors (two rows of pins, fifty total).

If you don't yet have the information you need, I can send you the
"ribbon cable order" of the DB-50 pins.


From: thad@public.BTR.COM (Thaddeus P. Floryan)

Your assumption is basically correct, but note that pin/wire number 1 is
the only common reference.

If you examine a Centronics-style 50-pin connector, you'll note that one
row of pins is labelled 1-25 and the other row is labelled 26-50.

If you examine the D-50 (with 17x16x17 pins), you'll note the "top" row is
labelled 1-17, the middle row is 18-33, and the bottom row is 34-50.

Assuming you're using IDC (Insulation Displacement Connector) style
connectors for both the Centronics and D-50 with ribbon cable, you'll have
NO problems as long as pin 1 of both connectors is "keyed" to the wire #1
(typically marked with a red stripe on grey ribbon) before clamping the
connectors onto the wire.


          pin 1 wire 1 pin 1
        __ / / __ /
       | | | |
       | | | |
       | | | |
       | | | |
       |__| |__|
      / / /
   pin 50 wire 50 pin 50

If you're using round cabling and solder-cup connectors, you will have to be
EXTRA careful to preserve the same "sense" of wire/pin orientation that would
exist if you had chosen to use ribbon cabling and IDC connectors.

Thad Floryan [ (OR) {decwrl, mips, fernwood}!btr!thad ]


From: lerman@stpstn.UUCP (Ken Lerman)

I'm reasonably sure that is NOT the way to wire the cable. When you
use such a connector with a ribbon cable, pin 1 goes to conductor 1,
pin 17 (or some such) goes to conductor 2, pin 33 goes to conductor 3,
pin 2 goes to conductor 4,...

I tried using a DG cable (don't know how it was wired) and IT didn't work.

Nu Data Inc has a cable which did work.
PHONE:(908)842-5757 FAX:(908)8421161
Centronics 50 Male to DB50 Male
#6418 18 inches $65.00
#6416 36 inches $75.00
#6417 72 inches $85.00

Nu Data has a catalog with the title SUNshine which is full of goodies
for Sun users. Tools, cables, terminators,...

No, I am not affiliated with Nu Data. I'm just a satisfied customer.

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