Kevin Vance posts on Twitter his design for a Commodore 64 cartridge using the inexpensive Raspberry Pi Pico microcontroller:
There are three buffer chips on the board to bring the 5V signals down to 3.3V.
When the C64 boots up, it’s reading a 16 KB window of the Pico’s RAM like it’s a ROM. This uses the Pico’s PIO and DMA controllers, so it takes a couple hundred nanoseconds, plenty of time for the Commodore’s 1 MHz clock.
The 6502 code stored in that window copies the 23 KB image displayer program to the C64’s memory in 1 KB chunks, then executes it.
Kevin plans to put up the PCB design, firmware, and assembly code on GitHub.
See more in the Twitter thread here.
I've taken another crack at putting a raspberry pi pico into a C64 cartridge, and it's exceeded my expectations pic.twitter.com/uBggBJqSo0
— Kevin Vance (@kvance) March 10, 2022
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