177 lines
6.0 KiB
ReStructuredText
177 lines
6.0 KiB
ReStructuredText
.. _pyb.UART:
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class UART -- duplex serial communication bus
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=============================================
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UART implements the standard UART/USART duplex serial communications protocol. At
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the physical level it consists of 2 lines: RX and TX. The unit of communication
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is a character (not to be confused with a string character) which can be 8 or 9
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bits wide.
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UART objects can be created and initialised using::
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from pyb import UART
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uart = UART(1, 9600) # init with given baudrate
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uart.init(9600, bits=8, parity=None, stop=1) # init with given parameters
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.. only:: port_pyboard
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Bits can be 7, 8 or 9. Parity can be None, 0 (even) or 1 (odd). Stop can be 1 or 2.
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*Note:* with parity=None, only 8 and 9 bits are supported. With parity enabled,
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only 7 and 8 bits are supported.
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A UART object acts like a stream object and reading and writing is done
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using the standard stream methods::
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uart.read(10) # read 10 characters, returns a bytes object
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uart.readall() # read all available characters
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uart.readline() # read a line
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uart.readinto(buf) # read and store into the given buffer
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uart.write('abc') # write the 3 characters
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.. only:: port_pyboard
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Individual characters can be read/written using::
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uart.readchar() # read 1 character and returns it as an integer
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uart.writechar(42) # write 1 character
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To check if there is anything to be read, use::
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uart.any() # returns True if any characters waiting
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*Note:* The stream functions ``read``, ``write``, etc. are new in MicroPython v1.3.4.
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Earlier versions use ``uart.send`` and ``uart.recv``.
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Constructors
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------------
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.. only:: port_pyboard
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.. class:: pyb.UART(bus, ...)
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Construct a UART object on the given bus. ``bus`` can be 1-6, or 'XA', 'XB', 'YA', or 'YB'.
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With no additional parameters, the UART object is created but not
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initialised (it has the settings from the last initialisation of
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the bus, if any). If extra arguments are given, the bus is initialised.
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See ``init`` for parameters of initialisation.
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The physical pins of the UART busses are:
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- ``UART(4)`` is on ``XA``: ``(TX, RX) = (X1, X2) = (PA0, PA1)``
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- ``UART(1)`` is on ``XB``: ``(TX, RX) = (X9, X10) = (PB6, PB7)``
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- ``UART(6)`` is on ``YA``: ``(TX, RX) = (Y1, Y2) = (PC6, PC7)``
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- ``UART(3)`` is on ``YB``: ``(TX, RX) = (Y9, Y10) = (PB10, PB11)``
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- ``UART(2)`` is on: ``(TX, RX) = (X3, X4) = (PA2, PA3)``
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Methods
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-------
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.. only:: port_pyboard
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.. method:: uart.init(baudrate, bits=8, parity=None, stop=1, \*, timeout=1000, flow=None, timeout_char=0, read_buf_len=64)
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Initialise the UART bus with the given parameters:
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- ``baudrate`` is the clock rate.
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- ``bits`` is the number of bits per character, 7, 8 or 9.
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- ``parity`` is the parity, ``None``, 0 (even) or 1 (odd).
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- ``stop`` is the number of stop bits, 1 or 2.
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- ``flow`` sets the flow control type. Can be None, ``UART.RTS``, ``UART.CTS``
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or ``UART.RTS | UART.CTS``.
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- ``timeout`` is the timeout in milliseconds to wait for the first character.
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- ``timeout_char`` is the timeout in milliseconds to wait between characters.
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- ``read_buf_len`` is the character length of the read buffer (0 to disable).
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This method will raise an exception if the baudrate could not be set within
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5% of the desired value. The minimum baudrate is dictated by the frequency
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of the bus that the UART is on; UART(1) and UART(6) are APB2, the rest are on
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APB1. The default bus frequencies give a minimum baudrate of 1300 for
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UART(1) and UART(6) and 650 for the others. Use :func:`pyb.freq <pyb.freq>`
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to reduce the bus frequencies to get lower baudrates.
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*Note:* with parity=None, only 8 and 9 bits are supported. With parity enabled,
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only 7 and 8 bits are supported.
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.. method:: uart.deinit()
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Turn off the UART bus.
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.. only:: port_pyboard
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.. method:: uart.any()
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Return ``True`` if any characters waiting, else ``False``.
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.. method:: uart.writechar(char)
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Write a single character on the bus. ``char`` is an integer to write.
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Return value: ``None``.
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.. method:: uart.read([nbytes])
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Read characters. If ``nbytes`` is specified then read at most that many bytes.
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.. only:: port_pyboard
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*Note:* for 9 bit characters each character takes two bytes, ``nbytes`` must
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be even, and the number of characters is ``nbytes/2``.
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Return value: a bytes object containing the bytes read in. Returns ``None``
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on timeout.
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.. method:: uart.readall()
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Read as much data as possible.
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Return value: a bytes object or ``None`` on timeout.
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.. method:: uart.readchar()
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Receive a single character on the bus.
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Return value: The character read, as an integer. Returns -1 on timeout.
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.. method:: uart.readinto(buf[, nbytes])
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Read bytes into the ``buf``. If ``nbytes`` is specified then read at most
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that many bytes. Otherwise, read at most ``len(buf)`` bytes.
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Return value: number of bytes read and stored into ``buf`` or ``None`` on
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timeout.
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.. method:: uart.readline()
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Read a line, ending in a newline character.
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Return value: the line read or ``None`` on timeout.
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.. method:: uart.write(buf)
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.. only:: port_pyboard
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Write the buffer of bytes to the bus. If characters are 7 or 8 bits wide
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then each byte is one character. If characters are 9 bits wide then two
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bytes are used for each character (little endian), and ``buf`` must contain
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an even number of bytes.
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Return value: number of bytes written or ``None`` on timeout.
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.. method:: uart.sendbreak()
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Send a break condition on the bus. This drives the bus low for a duration
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of 13 bits.
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Return value: ``None``.
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Constants
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---------
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.. only:: port_pyboard
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.. data:: UART.RTS
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.. data:: UART.CTS
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to select the flow control type
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