// Not all pins on the Mega and Mega 2560 boards support change interrupts,
// so only the following can be used for RX:
// 10, 11, 12, 13, 50, 51, 52, 53, A8 (62), A9 (63), A10 (64), A11 (65), A12 (66), A13 (67), A14 (68), A15 (69)

#include <SoftwareSerial.h>

SoftwareSerial mySerial(10, 9); //RX, TX

//#define mySerial Serial    // Hardwareserial Rx= 0 TX= 1
//#define mySerial Serial1   // Hardwareserial RX=15 TX=14
//#define mySerial Serial2   // Hardwareserial RX=17 TX=16
//#define mySerial Serial3   // Hardwareserial RX=19 TX=18

// 
                              
// 1  2  3  4  5  6 7  8 11 12 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31

void setup() {

  Serial.begin(9600);
  while (!Serial) {
    ;
  }

  mySerial.begin(4800);
  Serial.println("input command !");
}

void loop() {

  while (Serial.available()) {
    mySerial.write(Serial.read());
  }

  while (mySerial.available()) {
    Serial.write(mySerial.read());
  }

  // Add a short delay to avoid overwhelming the serial port
  delay(100);
}