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Re: Replacing the 6502 with a faster chip



Michael J. Mahon wrote:


Rob Jones replied:



mjmahon@aol.com (Michael J. Mahon) wrote in message
news:<20040820034253.26080.00002251@mb-m28.aol.com>...


Rob Jones wrote:



While surfing the 'net, I found this adaptor
(http://www.6502.org/mini-projects/816conv/conv.html) that replaces
the 6502 with a 65C816 processor. I have not done any research on the
65C816, or for that matter the 6502 and its variants, but is there a
way to replace the Apple's 1MHz processor with something faster?


I expect you want to know if you can make an Apple II run faster.

The answer is yes, but it takes a lot more than a faster processor.
The Apple II video generation is timed by the same clock that
creates the processor timing, and the peripheral bus must
operate at 1.0204 MHz for compatibility.  Some I/O cards
also require precise code timing for correct operation, most
notably the Disk ][ Controller for 5.25" disks.

So the trick is speeding up processing without changing the
bus or video timing and only when speeding up will not cause
other difficulties--not a simple problem.



<snip>


Is the 65C02 a pin-for-pin compatible with the 6502? I could very
easily make a 3X PLL (3MHz) to clock the "C" while keeping the bus at
1X (1MHz).



Simply clocking it faster will not allow it to interface with the
1MHz bus and memory interface.  You need to make the rest
of the Apple II _completely unaware_ that the processor is
running faster, which means that the fast processor must have
its own faster memory, either as an associatively mapped cache
or as a complete copy of the content of standard Apple RAM
(including any expansion memory if you want to run faster on
those accesses).

As I said, it is not a simple problem.  Modern FPGA's have
enough speed and complexity for a few-chip solution, but
the logic design is non-trivial.  I'm not aware of any publicly
available designs.

As Roy pointed out, anyone who manages to make, say, an
8MHz or faster Apple II accelerator for less than $80 will be
able to sell quite a few (I'd guess 50-100). 

I'd say perhaps 200 or more, esp. if sold via eBay.
One way to check is how well Bill Garber does with his memory card. And Bill, I may have a customer for you soon. New IIgs owner visited me yesterday and I showed him your webpage and found your eBay auction. 

If I needed one, I'd buy one from you.

Roy

Of course, that

price point would not be easy to hit...

-michael

Check out parallel computing for 8-bit Apples on my
Home page:  http://members.aol.com/MJMahon/




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