Mega2650 Pinouts

I have the Mega2650 listing of pin connections, and a pictorial of the board but can't figure out several pin connections:

1) what is IOREF ? - I don't see this on the pinout list

2) what are the six pins (double threes) next to the AREF pin?

3) are the unmarked connector pins connected to anything? e.g. the unmarked pin next to IOREF or the two next to AREF

Thanks, John

  1. what is IOREF ? - I don’t see this on the pinout list

This is a “new” pin added in the R3 series of Arduinos which is simply 5V to let shields know that underneath is a 5V system. Presumably other Arduino-like devices that operate at 3.3V can set this to 3.3V, similarly to let shields know that they are working on a 3.3V system.

  1. what are the six pins (double threes) next to the AREF pin?

Those are in-circuit programming (ICSP) pins for the USB microcontroller.

  1. are the unmarked connector pins connected to anything? e.g. the unmarked pin next to IOREF or the two next to AREF

The unmarked pin next to IOREF is not connected to anything. The two next to AREF are the TWI (I2C) pins, same as SDA/SCL pins 20 and 21.


The Rugged Audio Shield: Line In, Mic In, Headphone Out, microSD socket, potentiometer, play/record WAV files

what are the six pins (double threes) next to the AREF pin?

These are used for plugging in a programmer. These pins are also brought out to the connectors on the sides so there is no need to think you are missing something.

are the unmarked connector pins connected to anything?

No for the pin next to IOREF. The two next to AREF are the I2C bus. Again these are duplicates so a shield will know where the I2C bus is.

what is IOREF ? - I don't see this on the pinout list

The schematic shows it as just being connected to +5V, it is used by shields to distinguish between 3V3 and 5V boards.

Thanks for clearing this up; I appreciate it.

John-