int D=1000,ND=0;
int mode=0;
void setup() { 
  pinMode(13, OUTPUT);
  Serial.begin(115200);
}

void loop() {
  digitalWrite(13, HIGH);   
  delay(D);              
  digitalWrite(13, LOW); 
  Serial.print("Q=");
  Serial.println(D);
  Serial.print("T=");
  Serial.println(millis());
  delay(D);  
}
void serialEvent() {
  while (Serial.available()) {
    char inc = (char)Serial.read();
    if (mode==0 && inc=='D')  {
      mode=1;
      ND=0;
    }
    if (mode==1 && inc=='E'){
      D=ND;
      mode=0;
      ND=0;
      Serial.print("D=");
      Serial.println(D);
    }
    if (mode==1 &&(inc>='0'&& inc<='9')){
      ND=ND*10+(inc-'0');
    }
    if (mode==0 && inc=='Q')  {
        Serial.print("D=");
        Serial.println(D);
    }
  }
}