[vcf-midatlantic] 100Mhz 6502

Christian Liendo cliendo at gmail.com
Wed Oct 13 21:30:16 UTC 2021


The 100 MHz 6502

The 6502 was the CPU in my first computer (an Apple II plus), as well as
many other popular home computers of the late 1970s and 80s. It lived on
well into the 1990s in game consoles and chess computers, mostly in its
updated “65C02” CMOS version. Here’s a re-implementation of the 65C02 in an
FPGA, in a pin-compatible format that lets you upgrade those old computers
and games to 100 MHz clock rate!

Supported host systems

Chess computers
We have focused on Mephisto chess computers first, since these are at the
center of Roland’s collector’s interest. But many others are on the
wishlist, including Fidelity (Elite A/S Budapest and Glasgow, Prestige,
Avantgarde), Novag (Super Constellation, Super Expert C), SciSys
(Turbostar), …

Mephisto MM II and B&P
Mephisto MM IV, MM V, Rebel Portoroz (MM X)
Mephisto Polgar
Mephisto Milano and Nigel Short
Mephisto Rebell 5.0
Novag Constellation Forte A/B
Chafitz ARB (various Sargon versions) and MGS

So far, we are supporting the two 6502-based members of the classic 1977
“Trinity” of home computers – the Apple II and the Commodore PET series. It
may be possible and worthwhile to also support some slightly later
machines: The Acorn BBC Micro, Atari 400 and 800, and maybe the Commodore
C64 come to mind. I don’t have any of these computers though. Please
contact me if you are interested to help with an adaptation of the 65F02!

Apple II, including the II plus and europlus, and presumably the //e. Quite
a bit of hardware and software trickery by Steve Wozniak, and the older
models do not support a real 65C02 – but the 65F02 is a bit more generous
in its bus timing and works nicely. The Disk II floppy drive works nicely
under DOS 3.3; support for the language card is under development.

Commodore PET/CBM up to 8032. A very clean and “by the book” design. The
same memory map should work for all models from the PET 2001, the 3000 and
4000 series, and the 8000 series up to the 8032. (But excluding the 8096
and beyond, which require memory bank switching.) So far we have tested
this on the 8032 only; the 8050 floppy drive works.

A caveat is in order here. The home computers, with their flexibility and
expandability on both the hardware and software side, are bound to
encounter limitations and incompatibilities:

Memory expansion boards and bank switching need to be known to and emulated
by the 65F02; and since the 65F02 only has 64 kByte of RAM on board, it
cannot fully accelerate the extended memory. Also, while the 65F02 makes an
effort to detect the access to time-critical peripheral devices, and switch
back to the original slow speed temporarily, there will probably be
incompatible software or add-on hardware. And finally, some software you
simply don’t want to be accelerated – try an action video game at 100 MHz
to understand that concern…

The 65F02 supports an optional hardware switch to disable the acceleration.
This way, one can still select between accelerated operation and original
speed before one starts the host computer. In non-accelerated mode, the
65F02 should be fully compatible with any software or add-on hardware.
(Well; unless the software uses undocumented 6502 opcodes…

More information about the vcf-midatlantic mailing list