From: Baltissen, GJPAA (Ruud) (ruud.baltissen_at_abp.nl)
Date: 2003-11-21 15:12:00
Hallo allemaal,
I'm still busy with disassembling the ROM of my PC20-III. The reason why I
started this work was to find out how I can replace its HD with another
type. The only thing I can say is that until now it makes no sense :( AFAIK
it only uses four I/O addresses: 0320h..0323h, not the six I expect for a
normal IDE-HD. Even stranger is the following code:
; [AA79]
FillDX322_326 proc near
push cs
pop dx
cmp dh,0FAh ; CS = $FAxx?
mov dx,322h
jz loc_AA86 ; yes, ->
add dx,4 ; DX := $0326
loc_AA86:
in al,dx ; port 326h
retn
FillDX322_326 endp
The value used to fill DX depends on wether CS = 0FA00h or not! The only
time I know CS is 0FA00h is right after a reset when the PC is scanned for
"external" ROM with the well known "55 AA" identification code. For the
rest, I havent the faintest idea. The only thing I can think of adding
another IDE-interface with its own _same_ ROM which is executed on another
address.
Other info: AFAIK the interface is initialized by writing 6 values to the
same I/O address. This sounds like initializing a floppydrive. The only
thing I can imagine is that C= developed a floppy-like interface that on its
turn outputs IDE-signals. Any comment on this subject is very welcome.
PS: I have some vacation for a week so it is possible I won't react on react
on amy email untill december 1st.
--
___
/ __|__
/ / |_/ Groetjes, Ruud
\ \__|_\
\___| http://Ruud.C64.org
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