[Coco] Above 512k upgrades

[jdaggett at gate.net]

Mark

True. Still using the extra two bits above the six in the MMU is still doing a 
paging of 512K if you use 256Kx1 DRAMS. In theory there is a way to 
demultiplex the Z buss to use Static Rams and the refresh issue goes away. 

james

On 14 Aug 2007 at 6:55, Mark Marlette wrote:


> 

> 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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