Re: IIgs & ROMBANK

["Charlie" <charlieDOTd@verEYEzon.net>]

<mressl@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