char commanddata[2];
byte speeddata;

unsigned long time;
unsigned long c1timer;

int pwm_a = 6;  //PWM control for motor outputs 1 and 2 is on digital pin 3
int pwm_b = 9;  //PWM control for motor outputs 3 and 4 is on digital pin 11
int dir_a = 7;  //direction control for motor outputs 1 and 2 is on digital pin 12
int dir_b = 8;  //direction control for motor outputs 3 and 4 is on digital pin 13

void setup()
{
  // initialize the serial communication:
  Serial.begin(9600);
  Serial.setTimeout(3);

  pinMode(pwm_a, OUTPUT);  //Set control pins to be outputs
  pinMode(pwm_b, OUTPUT);
  pinMode(dir_a, OUTPUT);
  pinMode(dir_b, OUTPUT);

  analogWrite(pwm_a, 0);  //set both motors to run at (100/255 = 39)% duty cycle (slow)
  analogWrite(pwm_b, 0);
}

void loop() {
  byte command;
  byte relaycommand;



  // check if data has been sent from the computer:
  if(Serial.readBytes(commanddata,2)){
    // read the most recent byte (which will be from 0 to 255):
     command = commanddata[0];
     speeddata = commanddata[1];


  switch (command) {
  case 90:    // get software version   5a
    Serial.write(15);
    Serial.write(1);
    break;
  case 91:    // get relay states  5b
    //Serial.write(50);
    break;
  case 93:    // get relay states  5b
    Serial.write(50);
    break;
  case 100:    // motorA forward
    digitalWrite(dir_a, LOW);  //Set motor direction, 1 low, 2 high
    analogWrite(pwm_a, speeddata);
    c1timer=millis();
    break;
  case 101:    // motorB forward
    digitalWrite(dir_b, LOW);  //Set motor direction, 3 high, 4 low
    analogWrite(pwm_b, speeddata);
    c1timer=millis();
    break;
  case 102:    // motorA backward
    digitalWrite(dir_a, HIGH);  //Reverse motor direction, 1 high, 2 low
    analogWrite(pwm_a, speeddata);
    c1timer=millis();
    break;
  case 103:    //  motorB backward
    digitalWrite(dir_b, HIGH);  //Reverse motor direction, 3 low, 4 high
    analogWrite(pwm_b, speeddata);
    c1timer=millis();
    break;
  }

  }

    time = millis();
    if((time-c1timer)>500){
    analogWrite(pwm_a, 0);  //set both motors to run at (100/255 = 39)% duty cycle (slow)
    analogWrite(pwm_b, 0);
  }


}