Ice Man wrote:I've seen people using an Everdrive to run Ulitmate Mortal Kombat Trilogy for example. How exactly would this work since the game is 10MB or more by now.
Mega Everdrive generates its own /DTACK signal on the B20 pin when accessing the $800000-$9FFFFF area
Maximal supported size is 10MB, the 12MB ROM hack won't work.
Is there a way I can still access $A00000-$AFFFFF?
No because it will result in access conflict with Z80 area (which includes the FM chip) and I/O area. There is some room in the upper area that is not used by anything but it is advised that you do not put any usable data here in EPROM.
The 12MB UMK3 hack you are talking about has nothing there for example, and the program never tries to read from ROM at these addresses, it's simply wasted space in ROM.
Would connecting a 3rd EPROM work as well by just adding the /OE signal to the 10th pin of the 74LS139 shown in the schematic?
No, it won't work because you need a specific /CE for the third EPROM, the one in this schematic which uses either /ASEL (B26) or VA23 (B11) only covers $000000-$7FFFFF area.
Also, pin 10 of the 74LS139 triggers the whole $800000-$BFFFFF area, you would need two additional address lines and different decoding logic to skip the $A00000-$AFFFFF area.