I have a system that includes two ATMEGAs, one is run at 3.3V because it interfaces with the SD card. The other is run at 5V at max clock of 20Mhz. The 5V one has some of its GPIO lines (as output) connected to the 3.3V one's GPIO lines as input. The 3.3V should be OK with 5V input, that is, no need to level shifting or anything? I think so, but I just wanted to make sure there is no bad side effect or anything.
Thanks for your thoughts!