At 12:38 22-1-01 +0100, you wrote:
> > > Now I'm working in a new mapping routine which uses VRAM to store ROM
> page= s
> > > there. Thus, 128KB machines will be able to run some MegaROM games.
> >
> > You could also use the extended VRAM, some people have 192kB of VRAM in
> their
> > MSX2, like me. Then it would be finally used!
>
>Hmmm. It's not a bad idea. Some megaroms (like Kenpelen Chess) use
>all the 128KB VRAM, so there is no room to allocate any ROM page there.
>... except if you have 192KB :)
>
>I'll study how the extended VRAM works :)
Here's how the V9938 technical databook describes it which is already coded
to assembly here:
setExp: ld a,64 ; Set expansion ram
out ($99),a
ld a,128+45
out ($99),a
ld a,h ; Write address bits 14 and 15
rlca
rlca
and 3
out ($99),a
ld a,128+14
out ($99),a
ld a,l ; Write address LSB
out ($99),a
ld a,h ; Write remaining bits with access
specification
and 63
or b
out ($99),a
ret
resExp: ld a,0 ; Reset expansion ram
out ($99),a
ld a,128+45
out ($99),a
ret
I never found a suitable use for the expansion ram (as it is called
formally), so it could be useful now.
HL = Address (16-bits, bit 17 ignored), B = 0 for read, B = 64 for write.
You can read and write using port #0 ($98) and if you want to use vram
again then you should call resExp.
GreeTz, BiFi
Visit my Home Page at www.bifi.msxnet.org
mail me at: [EMAIL PROTECTED]
FTP: ftp.bifi.msxnet.org
ICQ #36126979
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