Re: IIgs & ROMBANK

["mressl@gmail.com" <mressl@gmail.com>]

On 7 abr, 18:03, "Charlie" <charlieD...@verEYEzon.net> wrote:
> <mre...@gmail.com> wrote in message
>
> c28053af-0e0d-4de8-a700-70789cd182ee@u3g2000hsc.googlegroups.com">news:c28053af-0e0d-4de8-a700-70789cd182ee@u3g2000hsc.googlegroups.com...
>
> > Hi there,
> > I can't remember the source, but somewhere I read that $C028 switches
> > the ROM bank that is visible at E0/C000.FFFF. Normally it is taken
> > from FF/C000.FFFF,
>
> I'm not seeing that here.
>
> > but according to what I read, when the ROMBANK
> > switch is accessed, this changes to FF/8000.FFFF.
> > Could somebody with a real Apple IIgs please try these commands after
> > booting and reseting:
> > CALL-151
> > FF/D000
> > E0/C028
> > D000
>
> Well OK,
>
> -----------------
> AFTER RESET (Apple IIgs ROM 01):
>
> ]CALL-151
>
> *FF/D000
>
> FF/D000:6F-o
> *E0/C028
>
> E0/C028:48-`
> *D000
>
> E0/D000:FF-.
> ---------------
>
> But I don't believe this is telling you anything about $C028.  Its only
> telling you that E0/D000 doesn't equal FF/D000 after referencing C028 in the
> monitor.  To see if C028 has any effect you have to look at the value in
> E0/D000 before *and* after referencing C028.  So...
> ---------------
>
> AFTER RESET:
>
> ]CALL-151
>
> *FF/D000
>
> FF/D000:6F-o
> *E0/D000
>
> E0/D000:FF-.
> *E0/C028
>
> E0/C028:A0-
> *D000
>
> E0/D000:FF-.
>
> ---------------
>
> Note that nothing has changed at E0/D000 by referencing E0/C028 but even so
> I'm still not sure this is a good test because somewhere in the back of my
> mind I think that the monitor can't be reliably used for this sort of test.
> I don't remember why (it does its own bank switching maybe?).
> Anyway, it would be better to write a program that tests the values before
> and after referencing (toggling) the $C028 softswitch.
> By the way on the IIc does it matter if it is a read or write to $C028?
>
> > I am working on another IIgs emulator, and am trying to be as accurate
> > as possible to the original.
>
> Good luck on your emulator.  I would think it would be very hard without
> having a real IIgs on hand to test against.
>
> Charlie
>
> > On Feb 14, 4:50 pm, "Charlie" <charlieD...@verEYEzon.net> wrote:
> >> <mre...@gmail.com> wrote in message
>
> >>9a93d4ad-5324-4e26-9606-64bb7e565501@v46g2000hsv.googlegroups.com">news:9a93d4ad-5324-4e26-9606-64bb7e565501@v46g2000hsv.googlegroups.com...
>
> >> > Hi there,
>
> >> > does anybody know what the ROMBANK switch (C028) does on a IIgs? On a
> >> > IIc it switches the A14 line for the ROM, but what does it do on a
> >> > IIgs?
>
> >> According to the Apple IIGS Firmware Reference (copyright 1987) page 280,
> >> the ROMBANK switch ($C028) is not used in the Apple IIGS.
>
> >> Charlie

hi again,

first, thanks for trying it out! And you are right, the test I sent
you doesn't work. Could you try this one instead? Thanks!

CALL-151
1000:AE 00 D0 AD 28 C0 AD 00
1008:D0 AC 28 C0 DA 20 DA FD
1010:68 20 DA FD 60
1000G

This is supposed to print 4 hexadecimal digits (2 bytes). If they
don't match it'll give me a clue to what is going on.

Thanks!

Marc.-