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.. currentmodule:: machine
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class SPI -- a Serial Peripheral Interface bus protocol
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=======================================================
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SPI is a serial protocol that is driven by a master. At the physical level,
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bus consistens of 3 lines: SCK, MOSI, MISO. Multiple devices can share the
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same bus. Each device should have a separate, 4th signal, SS (Slave Select),
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to select a particualr device on a bus with which communication takes place.
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Management of an SS signal should happen in user code (via machine.Pin class).
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.. only:: port_wipy
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See usage model of I2C; SPI is very similar. Main difference is
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parameters to init the SPI bus::
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from machine import SPI
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spi = SPI(0, mode=SPI.MASTER, baudrate=1000000, polarity=0, phase=0, firstbit=SPI.MSB)
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Only required parameter is mode, must be SPI.MASTER. Polarity can be 0 or
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1, and is the level the idle clock line sits at. Phase can be 0 or 1 to
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sample data on the first or second clock edge respectively.
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Constructors
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------------
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.. class:: SPI(id, ...)
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Construct an SPI object on the given bus, ``id``. Values of ``id`` depend
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on a particular port and its hardware. Values 0, 1, etc. are commonly used
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to select hardware SPI block #0, #1, etc. Value -1 can be used for
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bitbanging (software) implementation of SPI (if supported by a port).
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With no additional parameters, the SPI 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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Methods
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-------
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.. method:: SPI.init(baudrate=1000000, \*, polarity=0, phase=0, bits=8, firstbit=SPI.MSB, pins=(CLK, MOSI, MISO), sck=None, mosi=None, miso=None)
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Initialise the SPI bus with the given parameters:
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- ``baudrate`` is the SCK clock rate.
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- ``polarity`` can be 0 or 1, and is the level the idle clock line sits at.
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- ``phase`` can be 0 or 1 to sample data on the first or second clock edge
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respectively.
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- ``bits`` is the width in bits of each transfer. Only 8 of is guaranteed to be supported by all hardware.
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- ``firstbit`` can be ``SPI.MSB`` or ``SPI.LSB``.
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- ``pins`` is an optional tuple with the pins to assign to the SPI bus (deprecated, only for WiPy).
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- ``sck``, ``mosi``, ``miso`` are pins (machine.Pin) objects to use for bus signals. For most
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hardware SPI blocks (as selected by ``id`` parameter to the constructore), pins are fixed
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and cannot be changed. In some cases, hardware blocks allow 2-3 alterbative pin sets for
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a hardware SPI block. Arbitrary pin assignments are possible only for a bitbanging SPI driver
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(``id``=-1).
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.. method:: SPI.deinit()
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Turn off the SPI bus.
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.. method:: SPI.write(buf)
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Write the data contained in ``buf``.
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Returns the number of bytes written.
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.. method:: SPI.read(nbytes, *, write=0x00)
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Read the ``nbytes`` while writing the data specified by ``write``.
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Return the number of bytes read.
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.. method:: SPI.readinto(buf, *, write=0x00)
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Read into the buffer specified by ``buf`` while writing the data specified by
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``write``.
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Return the number of bytes read.
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.. method:: SPI.write_readinto(write_buf, read_buf)
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Write from ``write_buf`` and read into ``read_buf``. Both buffers must have the
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same length.
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Returns the number of bytes written.
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Constants
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---------
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.. data:: SPI.MASTER
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for initialising the SPI bus to master
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.. data:: SPI.MSB
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set the first bit to be the most significant bit
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.. data:: SPI.LSB
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set the first bit to be the least significant bit
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