i am trying to send data via Labview to my arduino board using serial communication.My problem is that the arduino reads only the first byte of sent data then when i change it ,it doesn't react.
For example when i start the communication i send '0' to arduino.I sees it.but while it is running i send '1' but it doesn't behave accordingly to it.
I noticed also that the board 'sees' sometime the new value after a random period of time.

    void setup() { 
      Serial.begin(9600); 
      pinMode(13,OUTPUT); 
     } 

  char data='F';
  void loop() 
    { 
   

       
 data=Serial.read();

 

 delay(50);
 if (data=='0')
  {
    digitalWrite(13,HIGH);
    delay(1000);
   digitalWrite(13,LOW);
 delay(1000);
 } 

if (data=='1')
 {
  digitalWrite(13,HIGH);
  delay(4000);
  digitalWrite(13,LOW);
  delay(4000);
 } 
 data='4';

           }