Re: Where does the "16 SECTOR" message come from?

[Tristan Mumford <xtristan.xmumford@xgmail.xcom>]

Michael J. Mahon wrote:

> sicklittlemonkey wrote:
>> On Feb 20, 6:52 pm, "Michael J. Mahon" <mjma...@aol.com> wrote:
>> 
>>>The slot ROM (256 bytes) clearly reads the disk to determine whether
>>>it is a 13-sector format or a 16-sector format, but the $C800 space
>>>deosn't appear to belong to the disk controller.
>> 
>> 
>> In fact, it looks like it's the slot code that's bank switched via a
>> store to $CX80. This should make it easier to dump. It detects the
>> disk type, and then stores this code at $800:
>> 
>> 800: LDA #$02 (#$03) ; bank number?
>> 802: STA $CX80 ; select bank
>> 805: LDA #$00
>> 807: JMP $CX52 ($CX53) ; print "16 (13) SECTOR"? ... ;-)
>> 
>> The values in parentheses are for 13 sector disks.
> 
> <Whack on side of head>  Thanks for reminding me that it *has*
> to bank switch the slot space, since that's the only way it
> can be compatible!
> 
> So the only different code is the "reset" 256 bytes, and
> after it runs, the slot code will be identical to either
> the 13-sector boot ROM or the 16-sector boot ROM...

Unless I'm mistaken, which is not entirely unheard of, I should just be able
to attack it by just poking to 0x180 (sorry about the C style hex notation.
Force of habit) and BSAVEing each 256 byte page. Sure they are probably
duplicates of the Apple disk ROMs, but it can't hurt to look, right?

Jorge said that it had a 2k ROM. I'm going to believe this statement. It
also means I'm curious of its contents, and how much of it can be accessed.

I'd be surprised if it's more than just the 3 pages, but curiosity drives
me!

Tristan.


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