Serial Ports (Serial1, Serial2, Serial3) — Maple v0.0.12 Documentation

### Navigation

- next
- previous |
- LeafLabs |
- Index »
- Complete Language Index »

# Serial Ports (`Serial1`, `Serial2`, `Serial3`)

This page describes how to use the built-in serial ports (also known as USARTs). For more information about serial ports, see USART.

Contents

- Getting Started
- Communicating Over Serial
- Function Reference
- Library Documentation
- Arduino Compatibility Note

## Getting Started

First, decide which serial port you wish to use, and connect its pins to the device you’re communicating with. (The TX and RX pins for a serial port are labeled on your board’s silkscreen; for example, serial port 2 has pins labeled “TX2” and “RX2”).

The variable for controlling a serial port is the word `Serial`, plus the serial port’s number. For example, you can control serial port 1 with the variable `Serial1`, serial port 2 with `Serial2`, and so on.

In order to get started using your serial port, you’ll first need to turn it on. Do this by calling your serial port’s `begin()` function, giving it the baud rate you wish it to communicate at. If you’re not sure what baud rate to use, 9600 is a safe (although slow) value to try. Put this call to `begin()` in your setup(), like in the following example:

    void setup() {
        // 9600 is the baud rate to use.  The baud rate determines how
        // fast the communication goes.
        Serial2.begin(9600);
    }

    void loop() {
        // Communicate using Serial2 here
    }

## Communicating Over Serial

Now that your serial port is set up, it’s time to start communicating.

One common use for serial ports is to print strings and other debugging information to a computer. You can print numbers or strings using `print()` and `println()`, like this:

    void printSomeInformation() {
        Serial2.print("First, print this string.  Then print a number: ");
        Serial2.print(42);
        Serial2.print(".  You can print floating point values, too: ");
        Serial2.print(3.14);
        Serial2.println(". Using println() instead of print() ends the line.");
        Serial2.println("This sentence starts on a new line.");
    }

This sort of communication can go both ways: you can send characters from a computer to a serial port as well. You can check how many characters are waiting for you to read using the `available()` function, and read them out one at a time using `read()`. The following example program uses these functions to “echo” back anything sent to `Serial2`:

    void setup() {
        Serial2.begin(9600);
    }

    void echoCharacter() {
        // Check to see if we have received any information.  numUnread
        // will hold the number of bytes we've received, but haven't
        // looked at yet.
        int numUnread = Serial2.available();

        // numUnread > 0 means that there are some unread bytes waiting
        if (numUnread > 0) {
            // Read a single byte out:
            byte b = Serial2.read();
            // And then print it back:
            Serial2.print(b);
        }
    }

    void loop() {
        echoCharacter();
    }

## Function Reference

This section gives a full listing of functions available for use with serial ports.

## Library Documentation

All of the `Serial[1,2,3]` objects are instances of the `HardwareSerial` class, which is documented in this section. (This means that you can use any of these functions on any of `Serial1`, `Serial2`, and `Serial3`).

class `HardwareSerial`

  Serial port class. Predefined instances are `Serial1`, `Serial2`, and `Serial3`.

void `HardwareSerial::``begin`(unsigned int baud)

  Set up a `HardwareSerial` object for communications. This method must be called before attempting to use the `HardwareSerial` object (typically, you call this in your setup() function).

void `HardwareSerial::``end`()

  Disables the USART associated with this object, allowing any associated communication pins to be used for other purposes.

unsigned int `HardwareSerial::``available`()

  Returns the number of bytes available for reading.

unsigned char `HardwareSerial::``read`()

  Returns the next available, unread character. If there are no available characters (you can check this with `available`), the call will block until one becomes available.

void `HardwareSerial::``flush`()

  Throw away the contents of the serial port’s receiver (RX) buffer. That is, clears any buffered characters, so that the next character read is guaranteed to be new.

void `HardwareSerial::``print`(unsigned char b)

  Print the given byte over the USART.

void `HardwareSerial::``print`(char c)

  Print the given character over the USART. 7-bit clean characters are typically interpreted as ASCII text.

void `HardwareSerial::``print`(const char* str)

  Print the given null-terminated string over the USART.

void `HardwareSerial::``print`(int n)

  Print the argument’s digits over the USART, in decimal format. Negative values will be prefixed with a `'-'` character.

void `HardwareSerial::``print`(unsigned int n)

  Print the argument’s digits over the USART, in decimal format.

void `HardwareSerial::``print`(long n)

  Print the argument’s digits over the USART, in decimal format. Negative values will be prefixed with a `'-'` character.

void `HardwareSerial::``print`(unsigned long n)

  Print the argument’s digits over the USART, in decimal format.

void `HardwareSerial::``print`(long n, int base)

  Print the digits of `n` over the USART, in base `base` (which may be between 2 and 16). The `base` value 2 corresponds to binary, 8 to octal, 10 to decimal, and 16 to hexadecimal. Negative values will be prefixed with a `'-'` character.

void `HardwareSerial::``print`(double n)

  Print `n`, accurate to 2 digits after the decimal point.

void `HardwareSerial::``println`(char c)

  Like `print(c)`, followed by `"\r\n"`.

void `HardwareSerial::``println`(const char* c)

  Like `print(c)`, followed by `"\r\n"`.

void `HardwareSerial::``println`(unsigned char b)

  Like `print(b)`, followed by `"\r\n"`.

void `HardwareSerial::``println`(int n)

  Like `print(n)`, followed by `"\r\n"`.

void `HardwareSerial::``println`(unsigned int n)

  Like `print(n)`, followed by `"\r\n"`.

void `HardwareSerial::``println`(long n)

  Like `print(n)`, followed by `"\r\n"`.

void `HardwareSerial::``println`(unsigned long n)

  Like `print(n)`, followed by `"\r\n"`.

void `HardwareSerial::``println`(long n, int base)

  Like `print(n, b)`, followed by `"\r\n"`.

void `HardwareSerial::``println`(double n)

  Like `print(n)`, followed by `"\r\n"`.

void `HardwareSerial::``println`()

  Prints `"\r\n"` over the USART.

void `HardwareSerial::``write`(unsigned char ch)

  Sends one character over the USART. This function is currently blocking.

  This is a low-level function. One of the `print()` or `println()` functions is likely to be more useful when printing multiple characters, when formatting numbers for printing, etc.

void `HardwareSerial::``write`(const char* str)

  Send the given null-terminated character string over the USART.

  This is a low-level function. One of the `print()` or `println()` functions is likely to be more useful when printing multiple characters, when formatting numbers for printing, etc.

void `HardwareSerial::``write`(void* buf, unsigned int size)

  Writes the first `size` bytes of `buf` over the USART. Each byte is transmitted as an individual character.

  This is a low-level function. One of the `print()` or `println()` functions is likely to be more useful when printing multiple characters, when formatting numbers for printing, etc.

int `HardwareSerial::``txPin`()

  Return the number of the TX (transmit) pin.

int `HardwareSerial::``rxPin`()

  Return the number of the RX (receive) pin.

## Arduino Compatibility Note

Unlike the Arduino, none of the Maple’s serial ports is connected to the USB port on the Maple board. If you want to communicate using the built-in USB port, use SerialUSB instead. You will need an additional USB-to-serial adapter to communicate between a USART and your computer.

License and Attribution

Portions of this page were adapted from the Arduino Reference Documentation, which is released under a Creative Commons Attribution-ShareAlike 3.0 License.

### Navigation

- next
- previous |
- LeafLabs |
- Index »
- Complete Language Index »