[Coco] Thexder RGB vs Composite Mode.

[Robert Gault]

Mark Ormond wrote:
> I just got a thexder cart that seems to only boot up into RGB mode. (Colors are screwed up with a composite monitor).
> I verified the behavior by loading the image in mess and trying both monitor types.
> The manual says hold down clear when powering up the system, but on my cart that doesn't seem to make a difference.
>
> Any suggestions?
>
> Thanks.
> Later,
> dabone
>

I don't have the cart so am limited to testing with MESS and a ROM image (which 
may be bad).

The initial few bytes of code include
  LDA #$FD
  STA $FF02
  LDA $FF00
  ANDA #$40
  STA $A5
which is a test for the CLEAR key. If MESS is set to CMP video and Thexder 
started, the energy line has wrong colors. If the MESS debugger is activated and 
a break point set for $C012, then one can set the content of $A5 to either $00 
or $40 as desired. You can't trust MESS to see the CLEAR key in this context.
When you force $A5=$00, the energy line in the game is close to the correct 
colors. However, that seems to be the only color changes made to the game.

Looks to me that the game is buggy regards CMP/RGB. What would be required would 
be to disassemble the game to find where the palette colors are set. Then you 
could find why only the colors for the energy line were changed and not the rest.