Why would a pin not go high on an Arduino?

Question

I'm using a SparkFun-built Arduino Pro Mini 3.3V / 8MHz. One thing I need it to do is toggle the gate pin on a MOSFET, and that's not working for some reason. Getting in there with a multimeter, I see that the voltage on the pin never goes HIGH. The only thing I have running on there is the following bit of code:

void setup()  {
  pinMode(A7, OUTPUT);
}

void loop() {
  digitalWrite(A7, HIGH);
}

Any thoughts on either configuration or electronics that could be causing this?

The pertinent part of the schematic is:

Answer 1

A6 and A7 are Analog Input Only. This is most likely what your are running into.

The TQFP package of the AtMega328 has 2 more inputs that the DIP package (A6 and A7), but they are analog input only. 1.1.9 in the datasheet.