I have been working on creating a stand alone atmega2560 arduino. When trying to program it with a serial adapter using the rx and tx pins nothing was happening. After a lot of debugging I found the problem was with the chip.
I found that the ones that worked said atmega2560 16AU 0721, the ones that did not work said Atmega2560 16AU 1241. When looking on eBay, i noted that the Atmega2560 16AU comes with many different versions of those last four numerals, does anyone know what the last four digits on top of the atmega2560 16AU mean?