I would like to use the most pins possible on my Due. I have read in a few places that some pins are duplicates?
I cannot read a pin schematic and make heads or tales of it. It says that D10 = D77 and D4 = D87... are those duplicates in the CODE, or on the physical board?
They are physically shared signals on the board. I think they are the only two lines shared in this way. All the other lines are mapped 1:1 with pins on the the SAM3X.
Followup: What about if I (additionally) use the dedicated SPI pins in the middle (for SPI)? What pins are those duplicates of?
You can use MISO, MOSI and SCLK on that connector, and they are not physically shared with other pins.
That is how I read the schematic, I am sure if I am wrong someone will correct me