class UART – duplex serial communication bus¶

UART implements the standard UART/USART duplex serial communications protocol. At the physical level it consists of 2 lines: RX and TX. The unit of communication is a character (not to be confused with a string character) which can be 8 or 9 bits wide.

UART objects can be created and initialised using:

from machine import UART

uart = UART(1, 9600)                         # init with given baudrate
uart.init(9600, bits=8, parity=None, stop=1) # init with given parameters

Supported parameters differ on a board:

Pyboard: Bits can be 7, 8 or 9. Stop can be 1 or 2. With parity=None, only 8 and 9 bits are supported. With parity enabled, only 7 and 8 bits are supported.

WiPy/CC3200: Bits can be 5, 6, 7, 8. Stop can be 1 or 2.

A UART object acts like a stream object and reading and writing is done using the standard stream methods:

uart.read(10)       # read 10 characters, returns a bytes object
uart.read()         # read all available characters
uart.readline()     # read a line
uart.readinto(buf)  # read and store into the given buffer
uart.write('abc')   # write the 3 characters

Constructors¶

class machine.UART(id, ...)¶: Construct a UART object of the given id.

Methods¶

UART.deinit()¶: Turn off the UART bus.

UART.any()¶

Returns an integer counting the number of characters that can be read without blocking. It will return 0 if there are no characters available and a positive number if there are characters. The method may return 1 even if there is more than one character available for reading.

For more sophisticated querying of available characters use select.poll:

poll = select.poll()
poll.register(uart, select.POLLIN)
poll.poll(timeout)

UART.read([nbytes])¶

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

Return value: a bytes object containing the bytes read in. Returns None on timeout.

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.

UART.write(buf)¶

Write the buffer of bytes to the bus.

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

UART.sendbreak()¶: Send a break condition on the bus. This drives the bus low for a duration longer than required for a normal transmission of a character.