int step = 0;
char* up = "up";
char* down = "down";
char* direction;

void setup() {
pinMode(6, OUTPUT);
Serial.begin(9600);
Serial.println("BEGIN");
Serial.println();
}

void loop() {

 if (direction==up && step<255) {
 analogWrite(6, step++);
 Serial.println(step);
 delay(5);
 }
 else {
  direction = down;
 }


 if (direction==down && step>0) {
 analogWrite(6, step--);
 Serial.println(step);
 delay(5);
 }
 else {
  direction = up;
 }

}