jdp@caleb.UUCP (Jim Pritchett) (01/22/91)
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!jdpgsteckel@vergil.East.Sun.COM (Geoff Steckel - Sun BOS Hardware CONTRACTOR) (01/23/91)
In article <2331.AA2331@caleb> jdp@caleb.UUCP (Jim Pritchett) writes: >I asked about putting my internal SCSI drives into an external box (Mini .....[list deleted].... >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. I'd strongly advise against doing this. The SCSI signals really need at least alternate grounds; twisted pairs are better. If you make the DB-25 to 50 pin cable adapter, put it at the Mac end, as close as possible to the DB-25. (Using the DB-25 violates the SCSI standard, but who cares about standards ....(:-)....) Use twisted pair (or twist'n'flat) if you're going to run more than a foot or two - this is both to protect your data and your peace. The SCSI cable will radiate a lot of RF to any nearby receiver if it isn't shielded. geoff steckel (gwes@wjh12.harvard.EDU) (...!husc6!wjh12!omnivore!gws) Disclaimer: I am not affiliated with Sun Microsystems, despite the From: line. This posting is entirely the author's responsibility.
mueller@hatteras.cs.unc.edu (Carl Mueller) (01/23/91)
In article <2331.AA2331@caleb> Jim writes: >... > 2. Buy a Mac SCSI cable and then direct connect it to 50 conductor > ribbon. (WRONG!) >... > >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? >... >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 At first I was going to say that I don't believe the cable you received is a proper Mac SCSI cable. However, I looked carefully at your pin-outs again, and realized that you may either 1) have the proper cable, but have mis-numbered your pins in making your pin-out, or 2) the cable company mis-numbered the pins on the pin-out. Think about it for a bit. The standard DB-type connector is numbered something like this: 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 The standard header connector is numbered like this: 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 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 The question now is, how was the Centronics-type AMP connector numbered in your diagram? Regardless of the numbering, all that matters is that the right pins on the DB-25 go to the right pins on the header (geometrically speaking). Check your cable again. I also predict that pins 10, 12, 14, and 15 on the "Mac" end do indeed go to one of the ground pins on the "Ext" end. Something to remember: The only reason Apple started with the non-standard DB-25 SCSI was to save connector space on the rear of the Mac Plus. It became a pseudo-standard which Commodore (among others) picked up. -Carl (mueller@cs.unc.edu)
billsey@agora.rain.com (Bill Seymour) (01/25/91)
In article <2331.AA2331@caleb> jdp@caleb.UUCP (Jim Pritchett) writes:
:
: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:
I haven't really cross checked your pinouts, but are you sure you're
not just looking at two different numbering schemes? The standard 50 pin SCSI
connector is numbered something like this:
01 03 05 07 ...
02 04 06 08 ...
and it's very possible the centronics type connector is numbered like this:
01 02 03 04 ...
26 27 28 29 ...
This might account for the pin number differences you see. I know that on my
3000, I was able to just use a standard Mac cable from the 3000 to the drive
case, and a ribbon cable with a 50 pin IDC connector and a 50 pin centronics
connector crimped on. This implies a 1:1 correspondence between the cables.
: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
--
-Bill Seymour billsey@agora.uucp or billsey@agora.rain.com
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