[Coco] CaChars - SCW-like screen characters for Color BASIC

[Robert Gault]

Juan Castro wrote:
> I'm only testing if the four upper bits of the PIA at $FF22 are all ones.
> Are you saying that can cause problems in the CoCo 3?
>
> I can't delve into CoCo code here at work, I'll take a look at that when I
> get home tonight. Meanwhile, what's the most canonical/portable way of
> testing whether I'm running in a CoCo 3? (So I don't try to hook CLS's
> vector if I am)
>
> Thx,
> Juan
>

Juan,

I found the problem, I think. The Coco3 patches the code at $A910 rather than 
using the link at $1A0. So that

$A910   jsr $1A0

becomes

$A910   jmp $8C46

That means your program will need to test for the presence of a Coco3, i.e. if 
$FFFE=$8C1B you have a Coco3. If there is a Coco3, you patch $A911-$A912. If 
there is not a Coco3, then you patch as you currently do $1A1-$1A2.

I'll change your source code and test it.

Robert