RP2040 and 5V Logic - Best Friends? This FX9000P confirms!

Over the years we have seen some modern microcontrollers prove to be 5V tolerant. Now the RP2040 joins the crowd. Six months ago when we were covering an ISA board based on a Pi Pico, [Eben Upton] left a comment saying that RP2040 is, technically, 5V tolerant for GPIO input purposes. The datasheets don't state this because the reality of 5V tolerance is not the same as native 5V tolerant chips - for example, it doesn't extend to 5.5V for it to be "legally" 5V tolerant, as in, what 5V tolerance usually means when mentioned in a datasheet.

After reading this comment, [Andrew Menadue] set out to test the GPIO capabilities of the RP2040, in a perfectly real-world scenario. He works with retro technologies like Z80-era computers, using RP2040 boards to replace entire RAM and ROM chips that died in his FX9000P. Not only do RP2040 driven replacements work wonders, but using RP2040 boards is also much cheaper than sourcing replacements for chips long out of production!

Previously, [Andrew] used level-shifting chips to interface the RP2040 with 5V systems, but he rebuilt a few of his models without level-shifting for the purposes of this experiment. Now, he reports that, so far, those tips have worked long-term without issue. With [Eben's] comment, this inspires confidence in our RP2040 forays and 5V inputs.

There are a number of important caveats to this, which you should read. Some major points - some GPIOs (like ADC ones) can't support it, GPIOs aren't 5V tolerant when set to output, and you shouldn't power GPIOs with 5V when the RP2040's VDDIO isn't. is not energized. [Andrew] reports such a case himself - one of his boards has lost all level shifts except the 8-bit address bus, which is driven by the CPU or the RP2040 at different times, and that would result in 5V on a GPIO output-set in the event of a conflict. Overall, if you're working with 5V logic and your application gets hacked more than business-critical stuff, you can also remove level offsets.

In the video, [Andrew] also shows off some RP2040-based replacement IC boards – there are follow-up videos on his channel and a GitHub repository if you want to learn more about them! All in all a surprise, sure, but welcome, making quick Pi Pico hacks even faster, and some RP2040 projects even easier to build - for example, who knows, maybe this board ISA powered by Pico may lose its CPLD. It's fine when we get a statement under the table with technical elaboration - otherwise we might need to break the curve tracer, like [Avian] did when confirming the ESP8266 5V tolerance.