#include <SoftwareSerial.h>
// declare second serial port with pin 10 and 11 for RX and TX pin
SoftwareSerial serial2(10, 11); // RX, TX

void setup() {
  Serial.begin(9600);  // start serial port between self and computer with 9600 baud rate
  serial2.begin(4800); // start software serial with other board with 4800 baud rate
}

// string to hold current message from the computer
String current_msg = "";

void loop() {
  // loop while there's data from other board
  while (serial2.available() > 0) {
    // send received data to computer
    char c = serial2.read();
    Serial.write(c);
  }
  // read data input by the computer
  while (Serial.available() > 0) {
    char c = Serial.read();
    if (c == '\n') {
      // newline means we've read the whole message
      // show what we've entered on the serial monitor
      Serial.print("me: ");
      Serial.println(current_msg);
      current_msg = ""; // reset the string
    } else {
      current_msg += c; // append the character to the string
    }
    serial2.write(c); // send the data to other board
  }
}