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Info on SCSI layout for 6100

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#1 somedude

  • 6502
  • LocationThe Great White North

Posted 03 February 2017 - 07:27 PM

Hello everyone,



The goal is to connect a hard drive to the 6100, as I got it without one.

I haven't been able to find any 50 pin drives, but I have a few 68 pin SCSI drives that I can play with.

Due to the insane prices on eBay and elsewhere for a M-M 50 to 68 pin adapter, upwards of $40 including shipping, I decided to take the fun route and make one.

The plan is to crimp on a 68 pin male connector onto a 50 pin ribbon, both of which I already have.


To ensure I won't mess up the Mac, I have a PCI card that I can plug into a PC and try out the setup.

I know it's a crazy plan, but it should be fun. And it's basically risk free (for the Mac). :-)


Now here's the reason for my post.

I would like to know if the SCSI bus on the 6100 is single-ended or differential.

It appears that the pinout is slightly different in the two cases, so I need to select the right one.

Since I only have 68 pin drives, the right pinout is even more important, as they can support SCSI-II and III.

I could also use advice on whether a direct/passive non-terminated 50 to 68 pin connection should work.


Thank you very much for any suggestions.

#2 NJRoadfan

  • 68000

Posted 03 February 2017 - 10:46 PM

By default all 50-pin buses are single-ended on Macs. The 68-pin drive you buy MUST have a jumper to run single-ended, most low voltage differential (LVD) drives have this jumper so it shouldn't be too hard to find something that works. High voltage differential (HVD) drives will not work, period. You also have to terminate the upper byte of the wide SCSI bus, otherwise the drive will likely not work. Also keep in mind you are limited to SCSI ID 0-7 as well.


If you can find one of these, its basically plug and play: http://www.disctech....yte-Termination


More notes here: https://www.scio.k12..._tutorial.htm#4


Building an adapter for this is NOT simple and will be quite tedious. The wire pitch of the 68-pin cables is much thinner than the IDC standard 50-pin cables, a simple crimping isn't going to happen.


Also post what model drive you are planning to use. The jumper markings differ between drives quite a bit.

Edited by NJRoadfan, 03 February 2017 - 10:48 PM.

#3 somedude

  • 6502
  • LocationThe Great White North

Posted 05 February 2017 - 04:35 PM

Hello and thank you very much for replying.

I have these drives to play with:

The WD has a Force SE jumper and so does the ST31whereas the ST34 has a termination enable jumper.

I know about the difference in wires but I was hoping to be able to maybe do it the other way around, attach 50 pin connectors to the 68 pin cable. I have one who's wires look "fat" enough to work.... maybe

Thanks again

#4 Compgeke

  • 6502
  • LocationFairfield, California

Posted 05 February 2017 - 07:23 PM

Try one of these instead with your 68 pin cable. It's the same setup I've run in a few SEs. http://www.ebay.com/itm/371310538092

#5 somedude

  • 6502
  • LocationThe Great White North

Posted 05 February 2017 - 09:00 PM

Thank you, but that's a female 50, won't fit on the cable.
I neet male to male for my application, that is why I wanted to make my own cable.

I will keep searching for a deal though.
So far they were crazy prices.

Edited by somedude, 05 February 2017 - 09:03 PM.

#6 Compgeke

  • 6502
  • LocationFairfield, California

Posted 06 February 2017 - 12:05 AM

Won't fit the cable but it will fit the motherboard instead. Plug that into the motherboard then run the 68 cable to the drive.

#7 somedude

  • 6502
  • LocationThe Great White North

Posted 06 February 2017 - 10:59 PM

Thank you, yes but that still forces me to add a second adapter for the CD drive.
That may still be easier though, it's worth a shot.

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