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From: jdp@caleb.UUCP (Jim Pritchett)
Newsgroups: comp.sys.amiga.hardware,comp.periphs.scsi
Subject: Re: cabling
Message-ID: <2331.AA2331@caleb>
Date: 21 Jan 91 20:21:03 GMT
Followup-To: comp.sys.amiga.hardware,comp.periphs.scsi
Organization: is sometimes desirable
Lines: 134


I asked about putting my internal SCSI drives into an external box (Mini
Tower PC type case.)  Specifically, I asked about cabling.

> What did you find out?

Well, I got several answers, one of which was incorrect.  Basically, they
were:

      1.  Make a cable.
      2.  Buy a Mac SCSI cable and then direct connect it to 50 conductor
          ribbon.  (WRONG!)
      3.  Buy a cable from X...

I used the A2090 manual to get the information for the A2090 connectors.  I
used an ohmmeter to get the Mac info from a Mac SCSI cable.  Here it is:

Signal  Int.    Ext.    Mac

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
Ground  34
ATN     32      17      41
Ground  30
Ground  28
Open    26
Ground  24
Ground  22
Ground  20
P       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
Ground  03
Ground  05
Ground  07
Ground  09
Ground  11
Ground  13
Ground  15
Ground  17
Ground  19
Ground  21
Ground  23
Open    25
Ground  27
Ground  29
Ground  31
Ground  33
Ground  35
Ground  37
Ground  39
Ground  41
Ground  43
Ground  45
Ground  47
Ground  49
Ground          07      16
Ground                  18
Ground                  19
Ground          09      20
Ground                  21
Ground                  22
Ground          14      01
Ground                  02
Ground                  03
Ground          16      04
Ground                  05
Ground                  06
Ground          18      07
Ground                  08
Ground                  09
Ground                  11
Ground          24      23
Ground                  24
Ground                  25
TPWR    -       25      38
Open                    10
Open                    12
Open                    13
Open                    14
Open                    15
Open                    17
Open                    35
Open                    36
Open                    37
Open                    39
Open                    40
Open                    42

The above list is somewhat redundant so that I can use sort (with colstart=n)
to get the list sorted by pin numbers for whichever connector that I want to
look at.

It should be obvious that suggestion 2 won't work since the Mac 50 pin connector
is obviously wired differently than the standard SCSI 50 pin connector.  I
wonder why Apple decided to make life difficult for themselves and the rest
of the world by being different?

Anyway, I guess that I'll use a straight through DB-25 cable to connect the
A2090 to the drive case.  Then I'll make a DB-25 to 50 pin connector cable
to attach it to the drives.  It shouldn't be too hard, although I was hoping
for an easier method (#2 would have been easier - but, Apple has done it
again!.)


Disclaimer:  to the best of my knowledge, the above is correct.  However, I
could have made an error.  Verify the above information before trying to use
it.  I am NOT responsible for any damage caused by other people's use or
misuse of this information.


Thanks to all who tried to help.

--

                                                Jim Pritchett


UUCP:  texsun.central.sun.com!letni!rwsys!caleb!jdp
 or    spudge.lonestar.org!caleb!jdp
 or    letni.lonestar.org!dms3b1!caleb!jdp