AGAIN: SD (FM) on PC (Was: Panasonic 8" Floppy Drive

From: Fred Cisin <>
Date: Sun Nov 21 20:26:37 1999

On Sun, 21 Nov 1999, Richard Erlacher wrote:
> I never gave this much thought because I have a compaticard, though I have
> never used it. I've taken it out of the box, though, hence the manual,
> floppy, and board are all in different (and unknown) places.

Ah, yes. We've all been there. I don't think that you'll really need the
manual, but if you do, several of us can help. I assume that the disk was
simply the current version of Uniform. If you have multiple versions,
save them all. Towards the end, they seemed to be having so many support
problems that they backed off from inclusion of several problematic
features, such as being able to read and write the wrong Head number field
on the second side of Kaypro DS disks.

> There's no doubt that the 765, which is the controller on which essentially
> all PC FD controllers is definitely SD capable, since it's also used in one
> of my S-100 systems where it does SD every day.
> Surely there's some way to fool the FDC, perhaps by talking to it directly
> to accomplish a few simple operaitons, which will enable you to read/write
> SD 8" diskettes. I say this because the data rate for SD 8" is the same as
> for DD 5-1/4, so the clock must be there. The rest has got to be software
> once you've got the cable made.

YES, the 765 can do FM.
YES, SOME FDC boards were appropriately designed.
NO, the OEM IBM boards could NOT do FM, even if you do the software and
cable. That is because IBM hardwired their board for MFM.
Some of the knockoffs of the 765, such as the 37C65 did not require any
additional wiring for doing FM.

Therefore, if you want to do FM, you either need
* a board with one of the variant (such as 37C65) chips, or
* one that has the FM/MFM pin wired up (such as the Compaticard), or
* modify the IBM board with a few minor trace cuts and added wires (such
as Flagstaff Engineering).

Fred Cisin            
2210 Sixth St.                  (510) 644-9366
Berkeley, CA 94710-2219
Received on Sun Nov 21 1999 - 20:26:37 GMT

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