Examples > Software Serial Library

Simple Software Serial

Arduinos have built in support for serial communication on pins 0 and 1, but what if you need more serial ports? The SoftwareSerial Library has been developed to allow serial communication to take place on the other digital pins of your Arduino, using software to replicate the functionality of the hardwired RX and TX lines. This can be extremely helpful when the need arises to communicate with two serial enabled devices, or to talk with just one device while leaving the main serial port open for debugging purpose.

In the example below, digital pins 2 and 3 on your Arduino are used as virtual RX and TX serial lines. Digital pins 4 and 5 are another virtual serial port. Only one software serial port can listen at a time. When starting multiple Software Serial ports, the most recent one called with serial.begin() is listening. To listen on another, you must call serial.listen() for the port you wish to receive data on.

Here, ss2 on lines 4 and 5 starts last. By default it is listening when the program starts. You want to listen on pins 2 and 3, named "ss", so you call ss.listen(). Once you receive a "?" on the serial port ss, you begin listening on ss2 and enter the loop().

Hardware Required

  • Arduino Board

Circuit

There is no circuit for this example. Make sure that your Arduino is attached to your computer via USB to enable serial communication.

image developed using Fritzing. For more circuit examples, see the Fritzing project page

Code

/*
  Software serial multple serial test

 Receives from the hardware serial, sends to software serial.
 Receives from software serial, sends to hardware serial.

 The circuit:
 * RX is digital pin 10 (connect to TX of other device)
 * TX is digital pin 11 (connect to RX of other device)

 Note:
 Not all pins on the Mega and Mega 2560 support change interrupts,
 so only the following can be used for RX:
 10, 11, 12, 13, 50, 51, 52, 53, 62, 63, 64, 65, 66, 67, 68, 69

 Not all pins on the Leonardo and Micro support change interrupts,
 so only the following can be used for RX:
 8, 9, 10, 11, 14 (MISO), 15 (SCK), 16 (MOSI).

 created back in the mists of time
 modified 25 May 2012
 by Tom Igoe
 based on Mikal Hart's example

 This example code is in the public domain.

 */

#include <SoftwareSerial.h>

SoftwareSerial mySerial(10, 11); // RX, TX

void setup() {
  // Open serial communications and wait for port to open:
  Serial.begin(57600);
  while (!Serial) {
    ; // wait for serial port to connect. Needed for native USB port only
  }


  Serial.println("Goodnight moon!");

  // set the data rate for the SoftwareSerial port
  mySerial.begin(4800);
  mySerial.println("Hello, world?");
}

void loop() { // run over and over
  if (mySerial.available()) {
    Serial.write(mySerial.read());
  }
  if (Serial.available()) {
    mySerial.write(Serial.read());
  }
}

See also