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

[sales at gimechip.com]

SCS = Spare Chip Select
The GIME can change the SCS to respond to FF5x externally and $FF4x 
internally - since the FDC chip needs FF4x, if you set it to internal, the 
FDC chip won't work in the FDC cart. $FF5x was used by DISTO M.E.B. in the 
SC-I & RAM Packs;

----- Original Message ----- 
From: "Brett Gordon" <beretta42 at gmail.com>
To: "CoCoList for Color Computer Enthusiasts" <Coco at maltedmedia.com>
Sent: Saturday, June 19, 2010 6:37 AM
Subject: [Coco] How does the SCS line / GIME Setting Work?


>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
>
> --
> Coco mailing list
> Coco at maltedmedia.com
> http://five.pairlist.net/mailman/listinfo/coco


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