// send an int from one serial to another serial. 

#define RXD1 16  
#define TXD1 17  
#define RXD2 21  
#define TXD2 22  
int a = 1;
// int a = -500;

void setup() {
  // put your setup code here, to run once:
  Serial.begin(9600);
  Serial.println("Hello, ESP32!");

Serial1.begin(9600, SERIAL_8N1, RXD1, TXD1);
Serial2.begin(9600, SERIAL_8N1, RXD2, TXD2);  //

}

void loop() {

 Serial.print("sending: ");
 Serial.println(a);
 Serial1.print(a);               // print a to serial 1 
 a++;
delay(500); 

  if (Serial2.available() > 0) { // Check if data is available to read on serial 2
    int b = Serial2.parseInt();  // Read the incoming integer on serial2 and store it in 'x'
    Serial.print("Received: ");
    Serial.println(b);           // Print the received integer to serial monitor
  }

delay(10); // this speeds up the simulation
}