Big Easy Driver won't reverse

**SOLVED ** It turns out my pin A4 was not working. I switched to pin A2 and this works fine now.

Here's some very basic code for driving a stepper motor using a Big Easy Driver.

In the example I write HIGH to the dir pin but for some reason regardless of whether I write HIGH or LOW the stepper motor turns in the same direction. I'm wondering if it's somehow related to the fact that I'm using an analog pin.

void setup() {    
#define PIN_STEP A5 
#define PIN_DIR  A4 
#define PIN_ENABLE  A3 

  pinMode(PIN_STEP, OUTPUT);
  pinMode(PIN_DIR, OUTPUT);
  digitalWrite(PIN_DIR, LOW);
  digitalWrite(PIN_ENABLE, LOW);

void loop() { 
    digitalWrite(PIN_STEP, HIGH);
    digitalWrite(PIN_STEP, LOW);