[Coco] Above 512k upgrades

[Mark Marlette]

james,

You kill me. (laughing here) I never said that paging the 512k was the issue.

I think you like to argue.... :)

Mark

Quoting 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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>>
>
>
>
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