ATMEGA328P-U Vs ATMEGA328-PU
Answer : The main difference is the bit before the - . That is, the 328 vs the 328P. The "P" there denotes "Picopower" which allows the chip to run at very low power consumptions. Basically the P version is a more modern version of the non-P chip. There are probably other internal differences too but you will have to check the datasheets thoroughly for those. Everything after the - is to do with the packaging and environmental grading of the chip. For example PU is a -40C to +85C grade DIP chip. ANR is a -40C to +105C grade TQFP chip, etc. If you see 328P-U then that's probably a fake chip. There's no such thing as single U suffix. There are three die types: 328 328P 328PB all have different signature bytes which may or may not impact loading code into them. Generally tho the programming software needs to know which part type is being used, at a minimum for installing bootloader code. Serial downloading may end up ignoring the signatur...