Hi, I used the Arduino Due as a base for my own board, and I'm having some problems with digital pin 4.
According to the pin mapping page ( http://arduino.cc/en/Hacking/PinMappingSAM3X ), pin 4 is "connected to both PA29 and PC26". However, it seems to be only connected to PC26: when I set pin 4 to HIGH, I get 3.3v out of PC26, but only 1.5v out of PA29. If I set pin 4 to LOW, PC26 is 0v but PA29 is still 1.5v (which makes me think it's floating).
Is anyone else seeing this? Is there a way I can alter the source to make sure to set BOTH pins? Where is the code that handles setting both pins when you call digitalWrite(4)?
Note that I think on the Due board, PC26 and PA29 are wired together, so PA29 appears to be correct but really it's just following whatever voltage PC26 is putting out. If you disconnect PA29 from PC26 (like on my board), I'm guessing you'll see it's floating as well.
Here's the sketch for testing:
void setup() {
int testPin = 4;
pinMode(testPin, OUTPUT);
digitalWrite(testPin, HIGH);
}