I'm trying to design my own arduino type board based on the atmega 2560. After looking at the diagram of the pinout on the mega PJ0 and PJ1 are used for hw serial 3 and the rest of the PJ pins are unused. Could I use PJ2+3 and PJ4+5 as additional serial connections?

 

What does data sheet say? Are they digital pins? Are they general purpose i/o pins?

Arduino uses 2560 and they have software serial library where they use gpio pins for serial coms.

 

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