SASI interface, SCSI devices...

From: Ethan Dicks <>
Date: Thu Feb 10 00:43:38 2005

On Thu, 10 Feb 2005 00:20:02 -0500, Peter Sjoberg <> wrote:
> Some other people have answered to the sw part but I have some hw info.
> A little while ago (early 80s) I was involved in converting our CP/M
> system from SASI to SCSI...

Interesting story... I noticed it because of a long-time project of
mine that I have yet to complete... extending the innards of the
Commodore D9060/D9090. As I mentioned elsewhere in this thread, the
D9060/D9090 drives have an internal SASI<->ST-506 board made by, IIRC,
Tandon. The drive mech is certainly Tandon (TM602S or TM603S... same
params except the 7.5MB drive has 6 heads, and the 5MB drive has 4
heads). The other piece of the puzzle is the "DOS board", with
Commodore ROMs to implement their "DOS", and two bit-banged interfaces
- one IEEE-488 to talk to the PET, and one SASI port to talk to the
bridge card (there are two CPUs in there, with shared memory, as was
common with Commodore disks).

So... I've always envisioned replacing the SASI bridge card and the
TM60[23]S with a modernish SCSI disk... there is a 16MB internal limit
on filesystem size (255 tracks of 255 sectors of 256 bytes), so pretty
much anything would do, as long as it could be talked to by a 1MHz
6502 with a non-controller-chip-type 50-pin port. I hadn't thought
about particular timing differences with any of the signals, nor had I
thought about parity. Thanks for mentioning those as potential

If this project would ever become more complicated than a new set of
ROMs, I'd probably just emulate the entire drive with something
modern, but as long as I could redo the firmware and hang, say, a 40MB
or 200MB SCSI disk inside the beast, it seems like a good return on
the investment of time.

Thanks again for giving me more things to chew on before finding them
out the hard way,

Received on Thu Feb 10 2005 - 00:43:38 GMT

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