[Coco] Above 512k upgrades

[Mark Marlette]

james,

As extra register are available they are not needed unless you go 
beyond 2MB limit. The MMU and it's task registers are 6 bits wide and 
all you have to do is tack on the 2 bits to each and then update your 
refresh cycle.

The CoCo can't refresh newer style memories with out a modification.

Mark



At 8/13/2007 07:37 PM, you wrote:

>On 13 Aug 2007 at 17:38, Gary Coulbourne wrote:
>
> >
> > On Aug 13, 2007, at 5:26 PM, Chester A Patterson wrote:
> >
> > > Does anyone know where one could purchase (paypal/plastic) a 1MB or
> > > more RAM upgrade kit for Coco3?
> >
> > How do these actually work?  I understand the MMU for the standard
> > 512k, but I must admit to being somewhat baffled with the larger
> > ones.  Do they provide an additional page table for mapping, or
> > something of the kind?  Thanks!
> >
> > Peace,
> > Gary
> >
>************************
>
>While the standard MMU will only access 512K RAM, there are methods to
>extend this. All are essentially paging 512K blocks of memory. The GIME
>chip has an unallocated registers at $FF96, $FF98, and $FF9B. One can
>use on of these bytes to act as a page register to select up to 256 banks of
>512K of RAM.
>
>The external board would have to do some address decode for what ever
>you wish. I believe the common used address is $FF9B.
>
>james
>
>
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>
>
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