From: blgardne@javelin.sim.es.com (Dances With Bikers)
Subject: SCSI DB-25/50 pin Centronics/50 pin header wiring table
Reply-To: blgardne@javelin.sim.es.com
Organization: Evans & Sutherland Computer Corporation
Date: Sun, 12 Apr 1992 16:00:56 GMT

koren@hpfcdc.fc.hp.com (Steve Koren) writes:
>I don't have the pinouts on the Amiga DB-25 connector, so I can't
>compare.  Does anyone have this they could send to me?

Here's a table of the pinouts of the two kinds of 50 pin SCSI
connectors, and the DB-25 SCSI connector. Note that the two 50 pin
connectors are physically wired exactly the same, they just have
different pin numbering systems. Also, since the DB-25 (Apple kludge)
connector has disposed of 24 valuable ground wires, don't try to run a
25 pin cable for any distance. Make (or buy) a very short 25-50 pin
adapter cable that ties all of the 50 pin grounds to the 25 pin grounds
(you'll have to wire several grounds to each ground on the DB-25). Then
run 50 wire cable for your long connections.

Another tip: Don't trust pre-built cables, especially if they were
inexpensive. I've seen several pre-built cables that took shortcuts on
the number of ground wires, and they caused me a lot of trouble until I
found that the cable was defective. The worst one I've seen was a 50 pin
Centronics male-male cable that had NO grounds wired from end-to-end,
the only ground connection was the foil shield.


Signal  Header  DB25    Centronics

I/O     50      03      50
REQ     48      01      49
C/D     46      15      48
SEL     44      19      47
MSG     42      02      46
RST     40      04      45
ACK     38      05      44
BSY     36      06      43
N.C.    34              42
ATN     32      17      41
Ground  30      07      40
Ground  28      09      39
TermPwr 26      25      38
Ground  24      14      37
Ground  22      16      36
Ground  20      18      35
Parity  18      20      34
7       16      13      33
6       14      12      32
5       12      11      31
4       10      23      30
3       08      10      29
2       06      22      28
1       04      21      27
0       02      08      26

Ground  01      24      01
Ground  03              02
Ground  05              03
Ground  07              04
Ground  09              05
Ground  11              06
Ground  13              07
Ground  15              08
Ground  17              09
Ground  19              10
Ground  21              11
Ground  23              12
Open    25              13
Ground  27              14
Ground  29              15
Ground  31              16
Ground  33              17
Ground  35              18
Ground  37              19
Ground  39              20
Ground  41              21
Ground  43              22
Ground  45              23
Ground  47              24
Ground  49              25

Grounds:
Head  1  3  5  7  9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43 45 47 49
Cent  1  2  3  4  5  6  7  8  9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25

Signals:
Head  2  4  6  8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46 48 50
Cent 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
-- 
Blaine Gardner @ Evans & Sutherland        580 Arapeen Drive, SLC, Utah 84108
blgardne@javelin.sim.es.com  uunet!javelin.sim.es.com!blgardne  BIX: blaine_g
DoD #46               My other motorcycle is a Quadracer.              FJ1200