Re: CPU-Replacement for die 264 series?

On 24/03/2012 19:03, Gerrit Heitsch wrote:
> On 03/24/2012 06:40 PM, Jim Brain wrote:
>> On 3/24/2012 10:43 AM, Gerrit Heitsch wrote:
>>>
>>> I did a bit of side by side comparision (see below). The only signal I
>>> have a bit of a problem with is how 'Gate In' influences R/_W:
>>>
>>> From the TED system manual:
>>>
>>> R/_W is latched by the Gate In line to synchronize between a DRAM
>>> memory cycle and the processor clock cycle. If AEC is low when Gate In
>>> makes a low to high transition, the R/_W line will go to a high
>>> impedance state until the next transition of Gate In and AEC is high
>>> prior to the transition.
>>>
>>> It shouldn't be difficult to make that work, but so far I haven't been
>>> able to come up with a small and simple circuit for it. It would be
>>> nice if 2 TTL chips were enough.
>> I think life would be simpler with a small GAL/CPLD and a 6502. As much
>> as there are plenty of 6510s around in 64s, I hate to rob them out of
>> units that might be fixable.
>
> Well, it's a choice... I do have a few spare 6510s and you can find a 
> lot of C64 with busted cases and/or keyboards.
>
>
>> A CPLD at least would be able to provide 8 bits of IO and the GATE_IN
>> functionality.
>
> It would also have to provide the tristate functionality for the 
> address bus since the original 6502 doesn't have that.
>
>  Gerrit
>
>
>       Message was sent through the cbm-hackers mailing list

I floated this same idea on Commodore Bounty before it closed down but 
it got limited support.  I think Bil posted that the early 264 
prototypes were built with a 6510 and a few flip-flops.

At the time I had about 5 264 machines which all had dead CPU's. Since 
then I acquired about 12 cpu's from a supplier in China at an 
extortionate price, so I do have a few spare if anyone's desperate...

Rob

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