[Coco] MPI question

[jdaggett at gate.net]

On 7 Jul 2008 at 13:54, Chuck Youse wrote:

> Ok, so I know that multi-paks had some sort of problem with the Coco
> 3, requiring a modification to the PAL - something to do with
> conflicts with the GIME.  As far as I can tell, the MPI only uses
> address FF7F - did it only partially decode and thus overlap with the
> GIME?  Or was there a different problem?
> 
> C.
|--------------------

The later model sof the MPI uses $FF7F. If I remember correctly the original MPI 
uses $FF9F to do slot switch. This conflicts with the GIME's Horizontal Offset 
register. There is another conflict that I am not familiar with.

The GIME chip knows when and where the MPU addresses anything within the 
64K memory map of the 6809. The internal registers to the GIME chip are at 
$FF90 to $FFDF. Also the GIME chip mirrors the PIA registers at $FF00 - $FF03 
AND $FF20 - $FF23.

james