Posted By
Gaia
on 2017-01-07
11:59:06
|  Re: Porting to Commodore Plus 4 of my game Genius, memory/bitmap mode questions..
Note that setting video address above $8000 without clearing the ROM bit will show you the garbage on the data bus, not ROM or RAM data. Bitmap address ROM/RAM location is controlled via bit#2 in $FF12. I am now a bit confused what you have actually done here since I quickly checked and both YAPE and plus4emu behaved like the real machine (although when the bitmap data is set to start from $E000 YAPE is not showing the TED and I/O area via the bitmap because of performance reasons but since this mode should not be used anyway, this known limitation is of little practical relevance). I need to have a more detailed look later.
EDIT: I confirm this is a bug in YAPE. Wow. Such a simple glitch and took so many years to be revealed... it occurs in case registers are written in a given order.
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