N* MDS-AD3 disassembly (LONG!)

From: Jim Battle <frustum_at_pacbell.net>
Date: Sun Feb 3 14:59:07 2002

At 01:49 PM 2/3/02 -0500, you wrote:
>I'm working on putting a diskette on my SOL
>and getting CP/M running on it. Anyway, from
>what I can tell, it seems that a NorthStar
>MDS-AD3 is a controller commonly found in a
>SOL. I've acquired one and I'm in the process
>of checking it out. I dumped the boot ROM and
>it doesn't look anything like what's on Jim
>Battle's page.

The one on my page is from a "clone" of the NS dual density disk
controller. The one I have was designed by Robert Hogg of
MicroComplex. It is really a clever piece of coding. Unlike the original
NS design, which requires changing a PROM to relocate the board and
apparently a different boot ROM, the MicroComplex board can be relocated
with some jumpers. The boot ROM is tricky and can execute from any base
address (that is a multple of 256). The boot sector and the BIOS for the
CP/M on my web site also automatically handle different base addresses for
the controller.

The source code on my web site for the boot rom, the boot sector, and the
bios are all my own reverse engineering efforts, so they aren't
gospel. Bob Stek sent me some original docs for the MicroComplex board; at
some point I'll put put up the original boot rom assemble with the authors
comments.


>So I have hand disassembled it
>(see below) and it does make sense, it is all
>8080 instructions. I don't know the history of
>this board, so it may have come out of a
>Northstar Horizon.
>
>I have two questions:
>
>1) Does this disassembly look reasonable?
>2) Will this run on a 2MHz 8080 (SOL) as opposed
> to a 4MHz Z80 (Horizon)?

When I have a little bit more time I will double check the code. It will
make a difference if the speed is too far off.

-----
Jim Battle == frustum_at_pacbell.net
Received on Sun Feb 03 2002 - 14:59:07 GMT