This page describes how to use the built-in serial ports (also known as USARTs). For more information about serial ports, see USART.
Contents
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:
leaflabs.com
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
}
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();
}
This section gives a full listing of functions available for use with serial ports.
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).
Serial port class. Predefined instances are Serial1, Serial2, and Serial3.
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).
Disables the USART associated with this object, allowing any associated communication pins to be used for other purposes.
Returns the number of bytes available for reading.
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.
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.
Print the given byte over the USART.
Print the given character over the USART. 7-bit clean characters are typically interpreted as ASCII text.
Print the given null-terminated string over the USART.
Print the argument’s digits over the USART, in decimal format. Negative values will be prefixed with a '-' character.
Print the argument’s digits over the USART, in decimal format.
Print the argument’s digits over the USART, in decimal format. Negative values will be prefixed with a '-' character.
Print the argument’s digits over the USART, in decimal format.
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.
Like print(c), followed by "\r\n".
Like print(b), followed by "\r\n".
Like print(n), followed by "\r\n".
Like print(n), followed by "\r\n".
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.
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.
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.
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.