Tags and keywords
All pins on the 3rd header of the Mega2560 only involve the ATmega2560 mcu chip or the ground GND, +5V, +3V3, and VIN nets:
 
Some pins of interest:
- The :NCjust means "no connection" and does nothing.
- The :IOREFpin is in fact just connected to the+5Vnet.
- The :RESETpin does eventually make it to the corresponding ATmega2560 pin, but it is part of a wider net involving also reset of the ATmega16u2, so it is mapped only to aRESETnet.
- Four of the digital I/O pins also act as JTAG test pins: TDI (Test Data In); TDO (Test Data Out); TCK (Test Clock); 4. TMS (Test Mode Select).
 
    
