#include <SoftwareSerial.h> // 

// constants won't change. They're used here to set pin numbers:
const int buttonPin = PA3;     // the thnumber of the pushbutton pin
const int ledPin = PA7;
const int rx = PA1;
const int tx = PA0;
bool flashing = false;

SoftwareSerial mySerial(rx, tx);

// variables will change:
int buttonState = 0;         // variable for reading the pushbutton status

void setup() {

  mySerial.begin(4800);

  // initialize the pushbutton pin as an input:
  pinMode(buttonPin, INPUT);
}

void loop() {
  // read the state of the pushbutton value:
  buttonState = digitalRead(buttonPin);

  // check if the pushbutton is pressed. If it is, the buttonState is HIGH:
  if (buttonState == LOW) {

    flashing = !flashing;

    if (flashing) {
      mySerial.write(1);
    }

    delay(1000);
  }
  if (flashing ) {
    if (mySerial.available() > 0) {
      mySerial.read();
      digitalWrite (ledPin, HIGH);
      delay (1000);
      digitalWrite (ledPin, LOW);
      mySerial.write(1);

    }
  }
}