#define DIR  19
#define STEP 20
#define PUSH 28

void setup() {
  // put your setup code here, to run once:
  pinMode(DIR, OUTPUT);
  pinMode(STEP, OUTPUT);
  pinMode(PUSH, INPUT_PULLUP);
}

void loop() {
  // put your main code here, to run repeatedly:
  digitalWrite(DIR, LOW);
  if(digitalRead(PUSH) == 0)
    digitalWrite(STEP, HIGH);
  else
    digitalWrite(STEP, LOW);
  delay(1); // this speeds up the simulation
}