[Coco] How does the SCS line / GIME Setting Work?

[Brett Gordon]

Thanks Guys!  That does clarify things for me.   It sounds like there's
usually no reason to play with the SCS setting much.  I'm assuming most of
the time the GIME's SCS setting should be set to 1,  as the internal SCS
line was never instituted by the 74138 chip?   So there's some argument as
to the internal GIME workings, but at least I understand the premis behind
the arguments.

Thanks!

On Sat, Jun 19, 2010 at 7:37 AM, Brett Gordon <beretta42 at gmail.com> wrote:

> I hope this isn't too silly of a question to ask.  I'm foggy on the
> workings of the SCS line and how the SCS setting on the GIME chip effects
> it.
>
> From what I gathered the SCS line is asserted when the address bus is from
> 0xFF40 and 0xFF5F.   I assuming it's a specialized address line used to
> "help" the FDC out. I'm assuming a FDC pack could do this itself if it
> wanted too.  I'm figuring Tandy wanted to make their FDC a bit cheaper, so
> added this line to the CoCo's Cart port.  Is there any other *regular* uses
> for this line?
>
> And exactly what does the GIME's SCS enable do in 0xFF90 ?  I seem to
> remember playing with this setting once, and my FCD software stopped
> working.  So if your GIME's SCS's bit in 0XFF90 is off, the SCS will never
> be asserted?
>
> Pardon my ignorance....
>
> --
> Brett M. Gordon,
> beretta42 at gmail.com
>



-- 
Brett M. Gordon,
beretta42 at gmail.com