I'm using an ATSAM4LC2A on a board and made a small program that simply toggles PA20, outputting a square wave. The MCU programs fine but I get no square wave on PA20. However, if I place a pullup resistor, I then get a square wave. It's as if that pin is only pulling down.
Then, if I do the same with PA05, it works fine with no pullup resistor. I checked, and PA05 is supplied by VDDANA, while PA20 is supplied by LCDA. I tried the same on PA19 and PA18, which are also supplied by LCDA, and same result.
I am indeed applying 3.3V to VLCDIN. I even tried to enable the LCD controller on its CR register to see if LCDA was dependent on that, but no result.
Is there something I'm missing here to get power to those I/O pins?