Q's about iNES mapper assignments

...Because all this compression was already in place, there was nothing left
for me to compress. I had to expand the ROM with a mapper chip to fit in the
English text. But, I only needed a really basic chip that simply doubles the
lower bank of program ROM as this is where all the 496 blocks of text are
stored. I would simply swap it based on which of the pieces of text need to
be displayed at any moment.

It turned out that Mapper 78, the Irem 74HC161/32 chip was perfect. With it
you could have any number of program banks replace the first program bank, but
not change the second program bank--exactly what I needed. You can switch
character banks with it too, but I didn't need that. Supposedly, "several
Japanese Irem titles use this mapper", but I could only find two.

* Uchuusen - Cosmo Carrier by Jaleco
* Holy Diver by irem

And they switch banks quite differently, so in reality they are actually two
completely different mapper chips. Holy Diver's mapper needed a special 256
byte table to work... yuck, I didn't have that kind of room to waste. But
Uchuusen's mapper, you simply load the bank number you want into register A
and then perform this 4 byte piece of code. Easy and efficient.

tay ;A8
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