Sunday, April 22, 2018

Patching the CoCo ROM, patch #1

In honor of CoCofest, I give you patch #1.  This just patches the multiply and it only uses 6809 code.
Don't bother disassembling it, the source code will get posted once I patch a few more things.

Yeah, I can get away with patching the CoCo 3 ROM from BASIC on this one.  Other patches will have to be an executable.  ONLY FOR THE COCO 3!

1 POKE 65497,0
2 AD=VAL("&HFA0C")
10 FORI=0 TO 64:READ B$:A=VAL("&H"+B$)
11 POKE AD+I,A:NEXT

REM $BB02 JMP $FA0C
20 POKE VAL("&HBB02"),VAL("&H7E"):POKE VAL("&HBB03"),VAL("&HFA"):POKE VAL("&HBB04"),VAL("&H0C")


30 DATA 32,79,E7,60,96,60,3D,ED,63,E6,60,96,5E,3D,ED,61,E6,60,96,5D
40 DATA 3D,ED,65,E6,60,96,5F,3D,E3,62,ED,62,EC,65,E9,61,89,00,ED,60
50 DATA EC,63,D3,15,97,16,D7,63,EC,61,D9,14,99,13,DD,14,A6,60,89,00
60 DATA 97,13,32,67,39



2 comments:

  1. FWIW, the patch is placed at $FA0C, Super Extended BASIC supposedly only uses $FE00-$FE69, but no promises that something won't interfere with the patch.

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