[Coco] reading the ROM on a CoCo 3

[Mike Pepe]

Robert Gault wrote:
> 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
>>
> 
> There should not be any problems but your question needs more details. 
> Is there an MPI in use? If so, what slots are occupied and with what packs?
> 
> Keep in mind that the default setting for a Coco3 is all RAM. That means 
> you probably want to switch to ROM mode when reading a pack. That means 
> Basic should not be used to do the reading. Write a short ml program 
> that goes to ROM mode, reads the pack, goes back to RAM mode, and then 
> returns to Basic.
> 

Hey Robert,

I'm trying out an EEPROM in the socket of an FD502. In order to modify 
it, I need direct access to the ROM.

I of course realize that I can't do this in basic, and I am testing in 
assembly.

Is there something I'm missing in the CoCo3's GIME registers that turns 
the ROM on or off? I thought switching the MMU off was all I needed to do.

-Mike