UART

The uart module lets you talk to a device connected to your board using a serial interface.

Functions

microbit.uart.init(baudrate=9600, bits=8, parity=None, stop=1, \*, tx=None, rx=None)

Initialize serial communication with the specified parameters on the specified tx and rx pins. Note that for correct communication, the parameters have to be the same on both communicating devices.

Warning

Initializing the UART on external pins will cause the Python console on USB to become unaccessible, as it uses the same hardware. To bring the console back you must reinitialize the UART without passing anything for tx or rx (or passing None to these arguments). This means that calling uart.init(115200) is enough to restore the Python console.

The baudrate defines the speed of communication. Common baud rates include:

  • 9600

  • 14400

  • 19200

  • 28800

  • 38400

  • 57600

  • 115200

The bits defines the size of bytes being transmitted, and the board only supports 8. The parity parameter defines how parity is checked, and it can be None, microbit.uart.ODD or microbit.uart.EVEN. The stop parameter tells the number of stop bits, and has to be 1 for this board.

If tx and rx are not specified then the internal USB-UART TX/RX pins are used which connect to the USB serial converter on the micro:bit, thus connecting the UART to your PC. You can specify any other pins you want by passing the desired pin objects to the tx and rx parameters.

Note

When connecting the device, make sure you “cross” the wires – the TX pin on your board needs to be connected with the RX pin on the device, and the RX pin – with the TX pin on the device. Also make sure the ground pins of both devices are connected.

uart.any()

Return True if any data is waiting, else False.

uart.read([nbytes])

Read bytes. If nbytes is specified then read at most that many bytes, otherwise read as many bytes as possible.

Return value: a bytes object or None on timeout.

A bytes object contains a sequence of bytes. Because ASCII characters can fit in single bytes this type of object is often used to represent simple text and offers methods to manipulate it as such, e.g. you can display the text using the print() function.

You can also convert this object into a string object, and if there are non-ASCII characters present the encoding can be specified:

msg_bytes = uart.read()
msg_str = str(msg, 'UTF-8')

Note

The timeout for all UART reads depends on the baudrate and is otherwise not changeable via Python. The timeout, in milliseconds, is given by: microbit_uart_timeout_char = 13000 / baudrate + 1

Note

The internal UART RX buffer is 64 bytes, so make sure data is read before the buffer is full or some of the data might be lost.

Warning

Receiving 0x03 will stop your program by raising a Keyboard Interrupt. You can enable or disable this using micropython.kbd_intr().

uart.readall()

Removed since version 1.0.

Instead, use uart.read() with no arguments, which will read as much data as possible.

uart.readinto(buf[, nbytes])

Read bytes into the buf. If nbytes is specified then read at most that many bytes. Otherwise, read at most len(buf) bytes.

Return value: number of bytes read and stored into buf or None on timeout.

uart.readline()

Read a line, ending in a newline character.

Return value: the line read or None on timeout. The newline character is included in the returned bytes.

uart.write(buf)

Write the buffer to the bus, it can be a bytes object or a string:

uart.write('hello world')
uart.write(b'hello world')
uart.write(bytes([1, 2, 3]))

Return value: number of bytes written or None on timeout.