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142 lines
4.8 KiB
142 lines
4.8 KiB
.. currentmodule:: machine
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.. _machine.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 machine 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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Supported parameters differ on a board:
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Pyboard: Bits can be 7, 8 or 9. Stop can be 1 or 2. With *parity=None*,
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only 8 and 9 bits are supported. With parity enabled, only 7 and 8 bits
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are supported.
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WiPy/CC3200: Bits can be 5, 6, 7, 8. Stop can be 1 or 2.
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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.read() # 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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Constructors
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------------
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.. class:: UART(id, ...)
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Construct a UART object of the given id.
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Methods
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-------
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.. only:: port_wipy
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.. method:: UART.init(baudrate=9600, bits=8, parity=None, stop=1, \*, pins=(TX, RX, RTS, CTS))
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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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- ``pins`` is a 4 or 2 item list indicating the TX, RX, RTS and CTS pins (in that order).
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Any of the pins can be None if one wants the UART to operate with limited functionality.
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If the RTS pin is given the the RX pin must be given as well. The same applies to CTS.
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When no pins are given, then the default set of TX and RX pins is taken, and hardware
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flow control will be disabled. If pins=None, no pin assignment will be made.
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.. method:: UART.deinit()
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Turn off the UART bus.
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.. method:: UART.any()
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Returns an integer counting the number of characters that can be read without
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blocking. It will return 0 if there are no characters available and a positive
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number if there are characters. The method may return 1 even if there is more
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than one character available for reading.
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For more sophisticated querying of available characters use select.poll::
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poll = select.poll()
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poll.register(uart, select.POLLIN)
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poll.poll(timeout)
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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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otherwise read as much data as possible.
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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.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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Write the buffer of bytes to the bus.
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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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longer than required for a normal transmission of a character.
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.. only:: port_wipy
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.. method:: UART.irq(trigger, priority=1, handler=None, wake=machine.IDLE)
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Create a callback to be triggered when data is received on the UART.
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- ``trigger`` can only be ``UART.RX_ANY``
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- ``priority`` level of the interrupt. Can take values in the range 1-7.
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Higher values represent higher priorities.
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- ``handler`` an optional function to be called when new characters arrive.
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- ``wake`` can only be ``machine.IDLE``.
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.. note::
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The handler will be called whenever any of the following two conditions are met:
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- 8 new characters have been received.
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- At least 1 new character is waiting in the Rx buffer and the Rx line has been
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silent for the duration of 1 complete frame.
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This means that when the handler function is called there will be between 1 to 8
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characters waiting.
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Returns an irq object.
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Constants
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---------
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.. data:: UART.RX_ANY
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IRQ trigger sources
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