[Coco] 64K Mode

jdaggett at gate.net jdaggett at gate.net
Tue Jan 13 15:40:08 EST 2004


Brad

In the SAM chip if you switch from memory map type 1 to type 0, by 
a write to $FFDE. you will now map the roms into memeory map. 
What info you have in the upper 32K can only be accessed in map 
type 0 by setting the page # byte, $FFD4 to clear the page register 
and $FFD5 to set the page register.. That will switch the 64K ram in 
two 32K pages. You code should be position independant. When in 
map type 1, all ram the page byte does nothing and the roms are 
not mapped. 

If you want to switch pages of graphics then you need to have you 
code running in rom at $C000 and use the lower 32K for grahics 
storage and program storage. You will have to switch the lower 32K 
bytes of ram in two pages. You now effectively have 96K machine. 

james


On 13 Jan 2004 at 10:55, Brad Grier wrote:

To:             	coco at maltedmedia.com
From:           	Brad Grier <bradgrier at cox.net>
Date sent:      	Tue, 13 Jan 2004 10:55:16 -0600
Subject:        	[Coco] 64K Mode
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> If I put a coco2 into 64k mode and then build and display a screen
> somewhere above memory location 0x8000, what would happen if I
> switched back out to 32k ram as the screen was being displayed? Would
> I see garbage on the screen or would the image persist?
> 
> The reason I ask is I'm working with a game that puts the intro
> screens in high memory and then rapidly switches out and back in to
> 64k mode while waiting for user input. I'm not sure if the game is
> synchronizing the bank switch with the display somehow or if the
> screen simply persists from 'high' ram perhaps until a new screen mode
> or offset is defined.
> 
> 
> 
> Brad
> 
> 
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