[Coco] MPI writing to $c000

[Darren A]

On Sun, Jan 24, 2016 at 9:14 AM, RETRO Innovations wrote:

> On 1/24/2016 8:44 AM, Robert Gault wrote:
>
>>
>> I doubt I can help with your PAK but the obvious issue that comes to mind
>> is whether you have set the MPI data at $FF7F correctly so that your
>> external ROM/RAM has access. After all, your device works when directly
>> connected to a Coco. :)
>>
> I hav put a scope on the WE line, and I am seeing the trigger, so I
> believe the correct slot is selected.
>
>>
>> The high nibble at $FF7F selects the MPI slot for RAM/ROM. The low nibble
>> selects the slot I/O at $FF40-$FF5F.
>>
>> Perhaps you meant that even with the MPI set to the correct slot for your
>> cart the RAM is not working. If that is the case, are you having failures
>> with any other cart that contains a ROM when plugged into the MPI?
>>
> All my MPI carts ROMs read fine.
>
>>

You may want to check if the address signals (A13 to A15) are making their
way through the MPI to the cartridge. Most ROM paks and disk controllers do
not use those address lines, so a connectivity problem with them would not
normally show up.

- Darren