[Coco] Question re: Cart slot decode

[Robert Gault]

Steven Hirsch wrote:
> On Mon, 2 Feb 2009, Stephen Castello wrote:
> 
>> On Mon, 2 Feb 2009 18:47:31 -0500 (EST), Steven Hirsch
>> <snhirsch at gmail.com> had a flock of green cheek conures squawk out:
>>
>>> I'm looking for a definitive answer on whether accesses between 
>>> ff60-ff7e
>>> are supposed to be decoded by the Multi-Pak and/or slot cartridges.
>>>
>>> All the docs seem to indicate that the SCS region is ff40-ff5f and the
>>> control register for the MP is at ff7f.  So, who owns the in-between
>>> addresses?
>>>
>>> I have a set of PAL equations for the older (large) MP that suggest it
>>> listens to the entire ff40-ff7f range, but it would be good to get a
>>> second opinion :-).
>>>
>>> From a 2001 email.  The list doesn't have everything that was made for
>> the Coco.
> 
>> FF60 \                  FF60 X position of pen
>> :     >   X-pad         FF61 Y position of pen
>> FF63 /                  FF62 Z pos/pressure of pen
>>                        FF63 ???
>>
>> FF68 \
>>      >   RS-232 pak 6551
>> FF6B /
>>
>> FF6C \
>> :     >   Modem Pak 6551 ACIA
>> FF6F /
>>
>> FF70 > alternate address of LR-Tech SASI controller
>> FF74 > default address of LR-Tech SASI controller
>>
>> FF70 \
>> :     > IDE controller alternate address
>> FF78 /
>>
>> FF7D \
>> :     >   Speech/Sound pak  FF7E speech chip register
>> FF7E /
>>
>> FF7F  >   Multi-Pak interface slot control switch (0=0,17=1,34=2,51=3)
>>
>> FF74 \
>> :     >   Disto SCII haltless controller additional addresses
>> FF77 /
>>
>> FF7A \                          FF7A left channel d/a
>> :     >   Orchestra 90-CC Pak   FF7B right channel d/a
>> FF7B /
> 
> 
> I guess that settles it.  There's a considerable quantity of erroneous 
> information out there, as I read about four different resources that 
> claim the SCS range is ff40-ff5f.
> 
> Thanks!
> 
> Steve
> 
> 

Steve H.,
Don't confuse the fact that many hardware devices use the region from 
$FF40-$FF7F with what SCS is supposed to do. If you credit the Tandy 
service manual for the Coco3 as being reasonably accurate, it says
"SCS* - This is a second chip select signal from IC9. (IC-9 is the 
74LS138.) It is active for both reads from and writes to addresses, 
$FF40 through $FF5F, regardless of map type."
Now since the Coco3 at $FF90 bit-2 controls the SCS (1=standard SCS), it 
makes one wonder what happens if that bit is turned off. I can't find 
any info on this in the service manual.

In any event, most of the devices mentioned in Stephen's message predate 
the Coco3. The SCS could not be turned off, made "non-standard".