int dir=7; int step=0;
void setup() {
  pinMode(13, OUTPUT);
  pinMode(dir, OUTPUT); digitalWrite(dir,HIGH);
}

void loop() {
  digitalWrite(13,HIGH);
  delayMicroseconds(10);
  digitalWrite(13,LOW);
  delay(100); step++;
  if (step>200/4) digitalWrite(dir,LOW);
  
  // put your main code here, to run repeatedly:

}