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 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
Bits can be
5, 6, 7, 8. Parity can be
UART.ODD. Stop can be
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 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.
On the GPy/FiPy UART2 is unavailable because it is used to communicate with the cellular radio.
Initialise the UART bus with the given parameters:
baudrateis the clock rate.
bitsis the number of bits per character. Can be
5, 6, 7 or 8.
parityis the parity,
None, UART.EVEN or UART.ODD.
stopis the number of stop bits,
1 or 2.
timeout_charsRx timeout defined in number of characters. The value given here will be multiplied by the time a characters takes to be transmitted at the configured
baudrate. The maximum value is 255
pinsis a 4 or 2 item list indicating the TXD, RXD, RTS and CTS pins (in that order). Any of the pins can be
Noneif one wants the UART to operate with limited functionality. If the RTS pin is given the the RX pin must be given as well. The same applies to CTS. When no pins are given, then the default set of TXD (P1) and RXD (P0) pins is taken, and hardware flow control will be disabled. If
pins=None, no pin assignment will be made.
rx_buffer_sizeis the size of the buffer used for storing the RX packets. By default is is 4096 bytes (characters). The minimum buffer size is 128 bytes.
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.
Return value: a bytes object containing the bytes read in. Returns
None on timeout.
Read bytes into the
nbytes is specified then read at most that many bytes. Otherwise, read at most
Return value: number of bytes read and stored into
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:
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