They are defined in the device header file, together with all other good stuff. A must read if you want to program a mcu.
Yes thanks, but how do I find the corresponding Arduino pin of PA3 ? In fact I would like to know, which "DDR" must be used for Arduino Mega's pins 22 to 53.
How do I find out which Arduino pins are related to for example DDRA on my Arduino Mega 2560?