[Coco] Re: atari USB device

[jdaggett at gate.net]

Mark

The main problem in making any USB cartridge backward compatible with the Coco 
1 and  Coco 2 is that Color Basic and Extended Color Basic set in ROM and that 
precludes any simple ram patch of the ROM code impossible. The Coco 3 copies all 
those ROMS into ram and can be patched rather easy. 

What has to be done is the cartridge would have to have the Color Basic and/or 
Extended Color Basic ROM modified and stored and decoded at address $A000 to 
$BFFF and/or $8000 to $9FFF along with the USB software at $C000. First 
estimates is that the KEYIN subroutine is all that is needed to be patched. In fact 
Color Basic 1.2 is easier to patch than Color Basic 1.0.  The KEYIN subroutine is 
where the computer looks at the PIA port and gets the value from it. 

It is not impossible but by far can be a bit more complex than that  of the Atari 
versin and more hardware. Definitely more cost.

just my wooden nickel  

james


On 24 Nov 2004 at 7:58, Mark Marlette wrote:

Date sent:      	Wed, 24 Nov 2004 07:58:26 -0600
To:             	jhoger at pobox.com,
	CoCoList for Color Computer Enthusiasts 
<coco at maltedmedia.com>
From:           	Mark Marlette <mmarlett at isd.net>
Subject:        	Re: [Coco] Re: atari USB device
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> USB keyboard. Remember that what ever is developed should be backwards
> compatible with the existing software. NitrOS-9 is not such a big deal
> but RSDOS is where the problem lies. The new USB driver would have to
> be in ROM/FLASH at power up and patch in not and not to step on
> anything else. Then get the USB stream from the keyboard via the
> hardware device, whatever that maybe and then emulate the software
> call that originally was in the CoCo. POLCAT, peeks of the keyboard
> port, etc...If not, you will find that your keyboard won't work with
> certain programs after you have the CoCo booted up and you are able to
> type from the command line via the USB. Double edge sword here. That
> is why the hardware solution into the keyboard port was the choice at
> Cloud-9. It can be done, just a few layers to sort out, the joy of the
> beast. :)