[Coco] CoCoNet status

[Darren A]

On 12/7/08, Roger Taylor rwrote:

>>
>>If you need to have Super Extended Basic available on the CoCo 3, you can
>> use
>>the same approach I used for Extended ADOS-3, which resides in a 27128.
>> When
>>you need to call a ROM routine that is in the upper 8K of your
>>EPROM, you switch
>>to ROM mode first, and switch back to ROM/RAM mode on the return from the
>>routine (to somewhere not in the upper 8K) to re-enable Super Ext. Basic.
>>(Have your ROM test whether it is running on a CoCo 3 during
>>initialization, and
>>do this only if a CoCo 3 is being used.)
>>
>>Art
>
>
> It seems like this should work on any CoCo using the same code.  Is
> there a reason why I should check whether it's a CoCo 3 or not?  I
> can understand if I'm having to use the GIME to do internal/external
> ROM switching and so forth to access the upper 16K of my ROM then
> CoCo 1,2 <> 3 checking might be necessary.
>
> --
> Roger Taylor

I think the reason is that on a CoCo 3, you will be running in ALL RAM
mode. The lower 8K of your EPROM ($C000-$DFFF) will have been copied
to RAM, but the upper 8K will not. When you need to call a routine in
the upper 8K, you first switch to ROM/RAM mode. When the call returns
you switch  back to ALL RAM mode. On a CoCo 1 or 2 with less than 64K
RAM you will not be able to copy your code from ROM to RAM, so doing
the switch back to ALL RAM mode would be deadly.

Darren