[Coco] Coco 3 Memory Map Questions

[William Astle]

On 2016-02-09 13:49, Arthur Flexser wrote:
> I'm not sure I understand the testing that led you to arrive at this
> conclusion.
>
> I'm a bit hazy on the order of the 2 halves of the 32K internal ROM.  Am I
> correct that the half with Extended Basic and Color Basic is the lower
> 16K?  If so, is it then the case that the 32 bytes in the ROM from $FFE0 to
> $FFFF (upper 16K) are duplicated at $BFE0-BFFF (lower 16K), the ending
> bytes of Color Basic?  If these two 32-byte ranges are exact duplicates of
> one another, how can you tell which is determining the hardware vectors,
> without burning a replacement ROM that modifies some bytes at one address
> or the other?  Or did you in fact do that?  (In your last sentence, you say
> this "could be done" by someone, which seems to imply that you did not do
> so.)

Yes, the internal 32K ROM is organized as you'd expect with ECB and CB 
in the lower half.

Only the 14 bytes from BFF2...BFFF and FFF2...FFFF are identical. FFE0 
through FFF1 do not match BFE0 through BFF1. It's extremely unlikely 
they would have specially mapped only 14 bytes. (You get 0000 at FFF0 
but at BFF0 is a couple of junk bytes.)

You're right that I haven't done the ROM experiement. At the time, I 
didn't have a machine with a socketed ROM and I don't have the skills to 
desolder chips and install sockets even if I did have EPROMs and a 
programmer.