Date   : Mon, 06 Oct 2008 20:45:57 +0100
From   : philb@... (Phil Blundell)
Subject: New 6502 second processors?

On Mon, 2008-10-06 at 20:14 +0100, Michael Firth wrote:
> Has anyone given any thought to producing replacement internal or
> external 6502 second processors?

I did think about this at one point, and I actually got as far as
building some PCBs with the appropriate circuitry on.  The idea was to
put the 6502 plus ULA emulation into a single FPGA - some kind of
Spartan-3 if I remember correctly, clocked at somewhere around 40MHz.
Aside from that you just needed an external SRAM, an EPROM, some bus
level translators and the power supply circuitry.  I think I also ended
up having to use a small XC9500 PLD to load the image into the FPGA, for
reasons which escape me at present.

Annoyingly though it turned out that I had gotten the PLD pinout
hopelessly wrong: I had somehow laid the board out for a TQFP device but
used the pin assignments from the PLCC part, or vice versa.  In any case
it would have required an inordinate amount of fiddly hand-wiring to
make the device fit, and I don't think I ever had the patience to do
that.

That was a couple of years ago now, and I suspect most of the parts I
used at the time are probably discontinued.  I'm pretty sure the RAM, in
particular, is impossible to buy now.  I keep thinking about having
another crack at that project but it would probably need to be more or
less redesigned from the ground up.

p.