Ongoing D9090 exploration

From: Ethan Dicks (
Date: 1999-10-09 00:15:04

Got it!  I found the spot in the 2K ROM code that checks for drive type and
adjusts the geometry.  I'm not sure if it is going to be feasible to change
yet (since I haven't found things like write-precomp or RWC), but if you
dig into a disassembly around $F8B0, X starts off at 6 and goes to 4 if PB5
is high.  The geometry data is stored around $049A as follows...

$049A: $98           highest numbered track (#152)
$049B: $03 or $05    heads-1

$049D: $04 or $06    heads
$049E: $20           sectors per track (256 byte sectors)
$049F: $04           ???

$04A0: $01           ???
$04A1: $00           ???
$04A2: $01

I'm thinking of just stuffing a 40Mb Quantum on my DOS board, doing a short
NEW and seeing if the drive likes the commands that come out.  It's not going
to damage the drive, but it might confuse it enough to require a power-off
reset, worst case.


Infinet has been sold.  The domain is going away in February.
Please send all replies to
Do You Yahoo!?
Bid and sell for free at
This message was sent through the cbm-hackers mailing list.
To unsubscribe: echo unsubscribe | mail

Archive generated by hypermail 2.1.1.