Okay, it looks like I've located the sections of pin assignments, and it's making vague sense. Now, it would be nice to have the pins in physical order instead of their port order, and I'm noticing that some pins have timers associated with them that aren't used. I also see that all four rx/tx serial ports use PWM (OSC[0..4][A..D]) pins- is this required hardware for the serial to work, or can any digital pin do the trick? On this graphic http://arduino.cc/en/Hacking/PinMapping2560, I see a mismatch- on the chip side, it has the four rx/tx ports scattered on all four sides of the chip, while the arduino pin map (red) has them grouped on the left edge. Does this say that those non-pwm pins can be used for rx/tx, too?