Have a look at this video. Piers does exactly what you're asking.
No level shifters are needed because, if you follow the rules, the RP2350's inputs are 5v tolerant.
He also explains exactly how he's programmed the PIOs to interact via DMAs to access the pico RAM.
I've got one of his 28 pin ONE-ROMs in my Master 128 and it works flawlessly in a sideways ROM slot. And I can reprogram it, in-situ, over USB-C even when the machine is still on. And because the ROM image is in flash it's persistent over power cycles.
No level shifters are needed because, if you follow the rules, the RP2350's inputs are 5v tolerant.
He also explains exactly how he's programmed the PIOs to interact via DMAs to access the pico RAM.
I've got one of his 28 pin ONE-ROMs in my Master 128 and it works flawlessly in a sideways ROM slot. And I can reprogram it, in-situ, over USB-C even when the machine is still on. And because the ROM image is in flash it's persistent over power cycles.
Statistics: Posted by Deflagration — Sun Feb 01, 2026 2:10 am