[Coco] Question re: Cart slot decode

[jdaggett at gate.net]

On 2 Feb 2009 at 18:07, Darren A wrote:

> > On Mon, 2 Feb 2009, Stephen Castello wrote:
> >
> > 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.
> 
> ---
> 
> Settles what?
> 
> The SCS range is FF40 - FF5F.
> 
> Darren
> 

The SCS is from $FF40 to $FF4F when the MC2 bit is "1".  When the MC2 
bit is "0" then the SCS is from $FF50 to $FF5F. 

The SCS line is only asserted for 16 bytes within the memory map. The 
MC2 bit selects which of two 16 byte ranges. This smacks of a potential of 
having two floopy controllers or a floopy and hard disk controller on one 
card. Access then can be done by just setting or clearing a bit in the INIT0 
register. of the GIME. Or even an internal and external floppy drive system. 

james
james