RE: D9090 ROM images uploaded to

From: Ethan Dicks (
Date: 1999-10-08 08:09:10

--- William Levak <> wrote:
> On Thu, 7 Oct 1999, Ethan Dicks wrote:
> As for the 9060/9090, this looks like a standard IEEE dual drive setup
> except that the 6530 is replaced by a 128x8 byte RAM(6810) and 2K ROM.


> The I/O functions of the 6530 seem to be done by the controller board.

Sort of.  Commodore/Tandon split those functions into a SASI portion
and a SASI to analog portion and used an off-the-shelf board to directly
control the drive.

> The manual says this has a 2900 series bit/slice processor(whatever that
> is).

The AMD 2900 was a 4-bit ALU (among other things) that was in common usage
in the early 1980s for implementing just about anything you wanted to.  I
have seen eight of them ganged together to implement the VAX-11/730 and four
of them in the vector coprocessor of the 6502-based arcade game Battlezone.

> Page 6 of the schematics(188008) show what looks like a processor
> and 4 memory chips.  However, the lettering on the schematics is
> unreadable.  The numbers from these chips would help.

My original C= copy is almost illegible, too.  It's not the scanner's fault;
it's Commodore for reprinting a copy of a copy of a copy.   

It's not explicitly labelled, but on 188008-006, part 9D appears to be
the AMD 2900 (at least it has the right number of pins - 40).  In any case,
it's not going to be fruitful to reverse-engineer the "controller" board.  It
is a standard (for 1982) SASI<->ST-506 adapter board like the Adapted ACB4000
is for SCSI<->ST-506.  I used to have a programmers manual for the board in
the D9060, but I haven't seen it in ten years.  The commands sent across the
bus are going to look a lot like SCSI-1 commands.  There is very little 
difference.  The trick is going to be identifying the code that manipulates
the 6522 and equating SASI signal names to bits in the VIA registers and then
seeing what kinds of commands are getting sent.  They are going to be
essentially READs, WRITEs and FORMATs.  That's all the farther we need to go.

I still think it's possible that once the 2K ROM is understood, it can be
reprogrammed to talk simple SCSI and drive a 20-50Mb drive with great
success.  I have enough spare parts that it's worth the effort to me.  I
even have a small box of DEC and Quantum 40Mb and 50Mb disks to throw at the


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