[Coco] replacing main rom

jdaggett at gate.net jdaggett at gate.net
Tue May 10 20:15:56 EDT 2005


To my knowledge I am not sure that the Coco 3 rom uses the timer for anything. At 
least when I plodded through the code to see how much space there was left in the 
Coco 3 basic. I looked to see h ow easy it would be to just rewrite the darn code and 
incorparate the 20+ patches. It is rediculous to see the startup have to patch a 
bunch of code to get it to run. I even wondered if there were a way to compress 
many of the same low resolution and high resolution basic cammands into one 
command. Like HSCREEN and SCREEN, LINE and HLINE.  

All the IRQs when passed through the GIME chip can be individually and locally 
disabled by writing a zero to the corresponding bits of $FF92 and $FF93. Clearing 
bits 4 and 5 of they INIT0 register($FF90) will globally disable all IRQs and FIRQs 
from the GIME chip. When that is done the IRQs from the PIA chips must be 
enabled in order to get any IRQs. 

I do like your idea of a Forth ROM for the Coco 3. Always wanted to play with that. 
The 6809 is excellent for it and the 6309 is even better with the extra registers. 


On 10 May 2005 at 16:51, John R. Hogerhuis wrote:

Subject:        	Re: [Coco] replacing main rom
From:           	"John R. Hogerhuis" <jhoger at pobox.com>
To:             	CoCoList for Color Computer Enthusiasts 
<coco at maltedmedia.com>,
	jhoger at pobox.com
Organization:   	Speaker To Machines, Inc.
Date sent:      	Tue, 10 May 2005 16:51:56 -0700
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> On Tue, 2005-05-10 at 13:28 -0700, John Hogerhuis wrote:
> > I've been reading through the super extended color basic manual to
> > figure out what needs to be set up on the coco at startup.
> > 
> err, hmm, I meant the super ECB unravelled book. The manual ain't much
> good for this kinda thing...
> Anyway I guess there's nothing Free around... to start I just need to
> write the minimal code to come up in 80-column hardware text screen.
> For now I can just poll the keyboard eventually though I will start
> adding interrupt handlers.
> Are there any interrupts that the coco must service for it to function
> normally?
> Looking at SEBU (super extended basic unravelled) I see
> TMR Timer interrupt
> HBORD Horizontal border interrupt
> VBORD Vertical border interrupt
> EI2 Serial border interrupt
> EI1 Keyboard interrupt
> EI0 Cartridge interrupt
> I'm thinking the GIME doesn't need any help to run the display, so I
> don't need to do anything special (other than return from interrupt)
> on HBORD and VBORD, right? 
> -- John.
> -- 
> Coco mailing list
> Coco at maltedmedia.com
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