Monotech's MOS CPU Replacer Turns a Humble 6502 Into a Drop-In 6510, 6510T, 8501, 8502 Equivalent
Pseudonymous New Zealand vintage computing enthusiast "Monotech" has launched a handy tool for those struggling to bring back MOS Technology-powered devices from the dead: A converter to turn a standard 6502 into a quartet of other far rarer chips.
The MOS 6502 is one of the most fondly-remembered microprocessors of its era, having powered devices from the best-selling Commodore 64 to the early Apple computers — and it's still in production today. Its lesser-known stablemates, however, are not: The 6510/8500 found in the Commodore 64, the 6510T in the Commodore 1551 floppy drive, the 8501/7501 in the Commodore 16, C116, and Plus/4, and the 8502 driving the Commodore 128.
"The above 'CPUs' are just standard 6502s with some extra logic tacked on inside," Monotech notes — which led to the creation of an adapter to pop that missing logic where it needs to go. "This device uses a standard 6502 CPU, and implements the extra functions using discrete logic — no programmable parts."
The idea is simple: Choose the chip type you're trying to replace, solder the jumpers accordingly to configure the external logic, and slot a 6502 chip home before popping the entire assembly into the CPU socket of your target device.
Operation in 6510 and 8501 modes have been confirmed as working, while the 6510T mode is untested; 8502 mode "works," its creator explains, "but has graphical glitches, likely due to a timing issue, so should only be built if you plan to help me diagnose this."
Another warning comes for those looking to use a more modern incarnation of the 6502, rather than period-appropriate original parts. "You can use a 65C02 or W65C02," Monotech explains, "but this is untested, and will cause compatibility issues with some software at the least, or not work at the worst."
KiCad files for the project have been published to GitHub under an unspecified license, while kit-form and fully-assembled boards are available with or without tested 6502 on the Monotech website starting at $15.