5V inputs on non-5V tolerant pins?

[RetroHQ]

I see the standard Gotek schematics connect 5V signals directly to non 5V tolerant GPIO pins. What is the longevity of this approach like? I realise inputs are open collector so the internal clamping diodes won’t be subject to much current, but it doesn’t seem like a good idea.

[keirf]

It's not a good idea, but the design has a long history and I haven't heard of any failures because of this flaw. Similarly, HC04 at vcc=5v is not the correct chip to interface to the MCU outputs, but in practice it works (as long as vcc doesn't get too high!).

I wouldn't design a board with this flaw myself and indeed, the 435-based Goteks I was involved in designing do not abuse the 5v intolerant pins. That said the AT32F435 has very few intolerant pins anyway!

I always recomment the 435 Goteks over 415 these days. The extra RAM makes certain operations and image types much more reliable.

[RetroHQ]

Thanks for the sanity check and that's a good overview of everything! I'm looking at potentially doing a custom board with STM32 + memory card and FlashFloppy for an Atari Falcon project. Is the STM32 capable enough for high density images and protected double density images? I'm pretty sure the answer is yes from my digging.

I've looked at the AT32F chips and I don't really want to have to get yet another programming tool and install another IDE if the STM will do just fine. I've used them before and already have the bits needed. :)