Donkey Kong, Jr. Bonus Timer Fix?

[ColecoFan1981]

I wonder how the check for the bonus timer is done in the CV Donkey Kong, Jr.? This also applies to the Adam Super Game release.

 

Starting bonus points:

5000 (screens 1-2)

6000 (screens 3-5)

7000 (screen 6+)

 

But what we also want...

8000 (screen 9+)

 

According to lightbulbsun at RomHackingDotNet, it went like this:
 

0x8851 -- 2E 37 -- LD L, 0x37 -- load tile for digit 7
0x8853 -- 06 70 -- LD B, 0x70 -- 7000, without the two trailing zeroes in BCD

 

For 8000 starting points on the timer, we'd change this to:
 

0x8851 -- 2E 38 -- LD L, 0x38 -- load tile for digit 8
0x8853 -- 06 80 -- LD B, 0x80 -- 8000, without the two trailing zeroes in BCD

 

But what about the rest of the timer that determines to stop it at where the original unmodified digit at 0x8851 is? Somewhere in the code we may find...

FE 05 -- CP #5 -- are we beyond screen 5 yet?

which we would change to

FE 08 -- CP #8 -- are we beyond screen 8 yet?

 

His suggestion...
 

0x8851 -- CD 00 C0 -- CALL $C000 
0x8854 -- 00       -- NOP        
0xC000 -- 2E 37    -- LD L, 0x37 ;replacement code
0xC002 -- 06 70    -- LD B, 0x70 ;that we've overwritten
0xC004 -- FE 08    -- CP #8      ;check if the screen is < 9
0xC006 -- D8       -- RET C      ;if so, set bonus to 7000 points
0xC007 -- 2E 38    -- LD L, 0x38 ;otherwise set first digit of bonus timer onscreen to 8
0xC009 -- 06 80    -- LD B, 0x80 ;and the bonus to 8000 points
0xC00B -- C9       -- RET

I find this to be ungainly because of the fact you have to search for empty ROM space or for orphaned commands that are not actually used in the game.

 

What I want to do is re-code this from scratch, to tell it we want to increase it normally every 1000 points up to the 9th screen, at which it begins at 8000 points.

 

~Ben

 

Edited June 27, 2023 by ColecoFan1981