[Coco] Some notes on ROM Paks
Boisy G. Pitre
boisy at boisypitre.com
Mon Apr 26 23:28:15 EDT 2004
As Art posted a few days ago, we've been having a private thread about
getting to the last 512 bytes of a ROM Pak (either 16K or 32K), or even
the 32K of CoCo 3 ROM.
Here are some conclusions that I've drawn from the discussion. Feel
free to prove or disprove them.
(1) On a CoCo 2, it is not possible to access the last 256 bytes of a
ROM Pak ($FFXX). Therefore, 16K ROM Paks do not have valid code in the
last 256 bytes.
(2) On a CoCo 3, it IS possible to access the last 512 bytes of a ROM
Pak ($FE00-$FFFF) through use of the MMU register trick as Art
(3) Even so, it is unlikely that CoCo 3 ROM Paks use the last 512 bytes
of the ROM Pak, unless the game uses the MMU register trick to get at
those last 512 bytes.
Assuming these hold true, then:
(1) It is safe to copy all but the last 256 bytes of a 16K ROM Pak into
a blank EPROM, and that game should run fine on a CoCo 1/2.
(2) It *may*, and in all likelihood *IS* safe to copy all but the last
512 bytes of a 16K or 32K ROM Pak from a CoCo 3 into a blank EPROM, and
that game should run fine on a CoCo 3.
(3) Since 16K ROM Paks designed for the CoCo 2 could possibly use the
second to last 256 bytes ($FEXX), such a PAK would NOT work properly on
a CoCo 3 since the CoCo 1/2 era Pak wouldn't know about the MMU or the
CoCo 3 (does anyone have an example of such a Pak?)
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