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Re: IIe Games That Don't Work on the IIgs



On 8/13/2011 9:51 AM, Tony Kavadias wrote:
On Aug 13, 6:45 pm, Antoine Vignau<antoine.vig...@laposte.net>  wrote:
There is: Alternate Display Mode. It shadows text page 2 and displays
it.
av

Yes, but there is a minor problem with using Alternate Display Mode:
the control panel sets up an interrupt generator for the IIGS to
interrupt every vertical blanking interval to copy High-Res Page 2
from bank $00 to bank $E0, making the games "stutter".  The reason for
this is because the Mega II does not shadow Page 2 text or high-
resolution Apple IIe graphics.

I've never heard that High-Res Page2 wasn't shadowed. It displays fine on my ROM 01 GS with Alternate Display Mode OFF. TEXT Page 2 doesn't.
There is even a register ($C035 bit 2) to turn on/off hires2 shadow.

I have a few games that appear to "fail" on the Apple IIGS because the
games use text Page 2 for some reason--often, this is just for showing
some text so as to configure things like how many players and whether
to use joystick or keyboard, but they revert back to Page 1 high-
resolution graphics in order to play the game.  I find myself enabling
Alternate Display Mode just for that period of time to read the text
display, but disabling it just to be able to play the game without
having sound generation and timing issues!

--tonza

Is it possible that what you are seeing is caused just by the Alternate Display Mode interrupting for Page 2 text even when it isn't being displayed?

Charlie