I just bought a Due board and am really impressed. I'm very new to electronics and I'm still trying to understand all of the 3.3V and 5V differences and ramifications.
// Pinout diagram
I'm a little confused about the SPI header. If the MOSI, MISO, and SCK pins can only handle 3.3V why does the SPI supply 5V?
It might be just for power. I have been having discussion about real time clock unit, it is powered by 5 volts, but for communication it can use other voltages (Logic 0: -0.3 to 0.8 volts; Logic 1: 2.2 to Vcc+0.3 volts). As you can see the communication voltages are not tied up to the voltage needed to power the device.
What you've explained makes a lot of sense. I used the SPI header to connect to a breakout board and it works just fine. Thanks!