UART implements the standard UART/USART duplex serial communications protocol. At the physical level it consists of 2 lines: RXD and TXD. The unit of communication is a character (not to be confused with a string character) which can be 5, 6, 7 or 8 bits wide.
UART objects can be created and initialized 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
Bits can be 5, 6, 7, 8. Parity can be None, UART.EVEN or UART.ODD. Stop can be 1, 1.5 or 2.
5, 6, 7, 8
None
UART.EVEN
UART.ODD
1, 1.5 or 2
A UART object acts like a stream object therefore reading and writing is done using the standard stream methods:
uart.read(10) # read 10 characters, returns a bytes object uart.readline() # read a line uart.readinto(buf) # read and store into the given buffer uart.write('abc') # write the 3 characters
To check if there is anything to be read, use:
uart.any() # returns the number of characters available for reading
from machine import UART # this uses the UART_1 default pins for TXD and RXD (``P3`` and ``P4``) uart = UART(1, baudrate=9600) uart.write('hello') uart.read(5) # read up to 5 bytes
from machine import UART # this uses the UART_1 non-default pins for TXD and RXD (``P20`` and ``P21``) uart = UART(1, baudrate=9600, pins=('P20','P21')) uart.write('hello') uart.read(5) # read up to 5 bytes
from machine import UART # this uses the UART_1 non-default pins for TXD, RXD, RTS and CTS (``P20``, ``P21``, ``P22``and ``P23``) uart = UART(1, baudrate=9600, pins=('P20', 'P21', 'P22', 'P23')) uart.write('hello') uart.read(5) # read up to 5 bytes
Construct a UART object on the given bus. bus can be 0, 1 or 2. If the bus is not given, the default one will be selected (0) or the selection will be made based on the given pins.
bus
0, 1 or 2
0
On the GPy/FiPy UART2 is unavailable because it is used to communicate with the cellular radio.
Initialize the UART bus with the given parameters:
baudrate
bits
5, 6, 7 or 8
parity
stop
1 or 2
timeout_chars
pins
pins=None
rx_buffer_size
Turn off the UART bus.
Return the number of characters available for reading.
Read characters. If nbytes is specified then read at most that many bytes. If not specified, it will read all bytes in the buffer.
nbytes
Return value: a bytes object containing the bytes read in. Returns None on timeout.
Read bytes into the buf. If nbytes is specified then read at most that many bytes. Otherwise, read at most len(buf) bytes.
buf
len(buf)
Return value: number of bytes read and stored into buf or None on timeout.
Read a line, ending in a newline character. If such a line exists, return is immediate. If the timeout elapses, all available data is returned regardless of whether a newline exists.
Return value: the line read or None on timeout if no data is available.
Write the buffer of bytes to the bus.
Return value: number of bytes written or None on timeout.
Send a break condition on the bus. This drives the bus low for a duration of 13 bits. Return value: None.
Waits at most timeout_ms for the last Tx transaction to complete. Returns True if all data has been sent and the TX buffer has no data in it, otherwise returns False.
timeout_ms
True
False
UART.RX_ANY