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

[Brett Gordon]

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