jdp@caleb.UUCP (Jim Pritchett) (01/25/91)
In article <700@borg.cs.unc.edu> mueller@hatteras.cs.unc.edu (Carl Mueller) writes: > 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? > It is numbered 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 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 > 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 Yes. > 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. > No, they don't. I checked this several times. (Including just now.) > 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. > Which is why I think that it is very dumb to shuffle the connections like they did. -- Jim Pritchett UUCP: texsun.central.sun.com!letni!rwsys!caleb!jdp or spudge.lonestar.org!caleb!jdp or letni.lonestar.org!dms3b1!caleb!jdp
jdp@caleb.UUCP (Jim Pritchett) (01/27/91)
In article <1991Jan24.175039.3477@agora.rain.com> billsey@agora.rain.com (Bill Seymour) writes: > 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. > Boy, do I feel stupid! You are correct. The pins correlate when you account for the different numbering schemes. I had noticed that they were different, but it simply did not register that this accounted for the "differences." Thank you for pointing out what should have been obvious, but wasn't. -- Jim Pritchett UUCP: texsun.central.sun.com!letni!rwsys!caleb!jdp or spudge.lonestar.org!caleb!jdp or letni.lonestar.org!dms3b1!caleb!jdp