 
 #define LED_PIN 13
 
-// serial input //
+// host communication //
 #define MAX_COMMAND 10
 #define BUF_SIZE 32
 byte buf[BUF_SIZE];

  byte pin = bctoi(1, 2);
  if (pin < 2 || pin > 10) { err(); return; }
  pinMode(pin, OUTPUT);
  if (buf[3] == '0') digitalWrite(pin, 0);
	else digitalWrite(pin, 1);
}

// 'digitalRead' command

byte motor2_target = MOTOR_VELOCITY_0;
byte motor_velocity = 30;
byte motor_velocity_increment = 5;
unsigned int motor_counter_start = 4000;
unsigned int motor_counter = 0;

//=======================================

void setup() 
{
  // unused pins
  pinMode(LED_PIN, OUTPUT);
  digitalWrite(LED_PIN, LOW);
  pinMode(2, INPUT_PULLUP);
