The 100 MHz 6502
The 6502 was the CPU in my first computer, 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! The idea is to use this as a "Universal" accelerator for 6502 and 65C02-based host computers - just plug it into the CPU socket. Roland's original interest was in 6502-based chess computers. We have successfully tested the prototype 65F02s in an Apple II and a Commodore 8032, as well as various chess computers. The tested computers include environments with TTL and CMOS logic levels, and clock rates ranging from 1 to 5 MHz. IRQs and NMIs are used in the hosts; some of the Mephisto chess computers actively use the READY signal to slow down the CPU, and the 65F02 respects that nicely. The chess computer community has put the 65F02 through its paces and found some very nice improvements in playing strength for the old chess computers.