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

[sales at gimechip.com]

Hey guys, don't flame me please, I just wanted to point out that the CoCo 3 
service manual states:
MC2=1=Standard SCS*

The Schematic in same manual has SCS* connected to output Y6 of the 74LS138.

Kevin Darlings GIME.TXT states:
Note: IF MC2=0, then XFF50-5F is SCS, and XFF40-4F will be internal to CoCo.

-----------------------------------------------------------------------------

FF90 INITIALIZATION REGISTER 0

Bit 7 - CoCo Bit 1= Color Computer 1/2 Compatible

Bit 6 - M/P 1= MMU enabled

Bit 5 - IEN 1= GIME IRQ output enabled to CPU

Bit 4 - FEN 1= GIME FIRQ " "

Bit 3 - MC3 1= Vector page RAM at FEXX enabled

Bit 2 - MC2 1= Standard SCS

Bit 1 - MC1 ROM mapping 0 X - 16K internal, 16K external

Bit 0 - MC0 " " 1 0 - 32K internal

1 1 - 32K external

CoCo bit set = MMU disabled, Video address from SAM, RGB/Comp Palettes => 
CC2.

-----------------------------------------------------------------------------

and also:

S2-0 = (address select code -> 74LS138) :

000 -0- ROM 010 -2- FF0X, FF2X 100 -4- int SCS 110 -6- norm SCS

001 -1- CTS 011 -3- FF1X, FF3X 101 -5- n/a 111 -7- ??ram??



======================================================



This seems to agree with the CoCo 3 Service Manual, and indicates:

MC2=1=SCS=$FF40-$FF5F

MC2=0=SCS=$FF50-$FF5F

with SCS* being Y6 of the 74LS138. When MC2=0, Y4=$FF4x and Y6=$FF5x

This seems to agree with Darren A.

-John

----- Original Message ----- 
From: <jdaggett at gate.net>
To: "CoCoList for Color Computer Enthusiasts" <coco at maltedmedia.com>
Sent: Saturday, June 19, 2010 11:00 PM
Subject: Re: [Coco] How does the SCS line / GIME Setting Work?


> On 19 Jun 2010 at 23:26, Gene Heskett wrote:
>
>> James, Kevin has been wrong before, and in fact that was the reason I put 
>> on
>> my bulletproof stuff and started on RBF.MN all those years ago, even 
>> before
>> the 6309 was discovered.  The level2 version was not doing exactly as the
>> docs said it should, so I fixed that code in 7 or 8 different locations
>> before I got to Ed34 and thought I was done.  But that one had a land 
>> mine
>> in its FD.SEG(48) handling that I put in :(, so now we've had 2 or 3 more
>> versions since.
>
> Gene
>
> I will say this. It was not my intent to say anyone is right or wrong even 
> though it may well
> have come out like that. Like I said I defered to his measurements until 
> otherwise I can prove
> myself either right or wrong. For now it makes little or no difference to 
> me.
>
> The GIME chip does not do everything the same as the SAM chip. There are a 
> lot of
> similarities and there are differemces. I will leave at that.
>
> james
> james
>
> --
> Coco mailing list
> Coco at maltedmedia.com
> http://five.pairlist.net/mailman/listinfo/coco


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