[Coco] reading the ROM on a CoCo 3

[Mike Pepe]

Oh, duh!

Forgot about the old SAM ROM/RAM switch.

Interestingly enough, when I do that, the program immediately crashes.

I'm loading the short code in $0E00, the machine has 512k. First thing 
it does is disable the interrupts.

Soon as I sta $ffde, the machine locks up and the screen fills with crap.

maybe I need to move the code to a different location.




Arthur Flexser wrote:
> This is doable under BASIC by POKE&HFFDE,0, which switches in the ROMs, prior to
> doing the read.  (You need to do this from a 32-column screen, since you'll be
> switching out Super Extended Basic's RAM drivers for the 40/80 column screens.)
> That will get you $C000-FDFF.  If you need $FE00-FEFF as well, there's a bit in
> one of the GIME registers ($FF90? $FF91?) that enables you to switch off "always
> RAM at $FE00" mode, though you probably need to disable the IRQ first to avoid a
> crash (POKE &HFF03,&H34), since you'll be switching out interrupt vectors.
> 
> Art
> 
> On Thu, 27 Jul 2006, Mike Pepe wrote:
> 
>> Hi guys,
>>
>> Does anyone know how to read the cartridge ROM directly on a CoCo 3?
>>
>> Whenever I try, I read the RAM copy. There is no activity on the cart's 
>> ROM select.
>>
>> I tried setting $FF90 to $8C, thinking that would switch off the MMU and 
>> go directly to the hardware, but doing reads results in nothing.
>>
>> The only time I get read activity on that cart select pin is after reset.
>>
>> What's the trick?
>>
>> -Mike
>>
>> -- 
>> Coco mailing list
>> Coco at maltedmedia.com
>> http://five.pairlist.net/mailman/listinfo/coco
>>
> 
>