Commit a0b2f48c authored by Paul Sokolovsky's avatar Paul Sokolovsky
Browse files

docs/machine.SPI: Bring up to date with Hardware API, make vendor-neutral.

parent c8d31585
.. currentmodule:: machine
class SPI -- a master-driven serial protocol
============================================
class SPI -- a Serial Peripheral Interface bus protocol
=======================================================
SPI is a serial protocol that is driven by a master. At the physical level
there are 3 lines: SCK, MOSI, MISO.
SPI is a serial protocol that is driven by a master. At the physical level,
bus consistens of 3 lines: SCK, MOSI, MISO. Multiple devices can share the
same bus. Each device should have a separate, 4th signal, SS (Slave Select),
to select a particualr device on a bus with which communication takes place.
Management of an SS signal should happen in user code (via machine.Pin class).
.. only:: port_wipy
......@@ -21,31 +24,37 @@ there are 3 lines: SCK, MOSI, MISO.
Constructors
------------
.. only:: port_wipy
.. class:: SPI(id, ...)
.. class:: SPI(id, ...)
Construct an SPI object on the given bus, ``id``. Values of ``id`` depend
on a particular port and its hardware. Values 0, 1, etc. are commonly used
to select hardware SPI block #0, #1, etc. Value -1 can be used for
bitbanging (software) implementation of SPI (if supported by a port).
Construct an SPI object on the given bus. ``id`` can be only 0.
With no additional parameters, the SPI object is created but not
initialised (it has the settings from the last initialisation of
the bus, if any). If extra arguments are given, the bus is initialised.
See ``init`` for parameters of initialisation.
With no additional parameters, the SPI object is created but not
initialised (it has the settings from the last initialisation of
the bus, if any). If extra arguments are given, the bus is initialised.
See ``init`` for parameters of initialisation.
Methods
-------
.. method:: SPI.init(mode, baudrate=1000000, \*, polarity=0, phase=0, bits=8, firstbit=SPI.MSB, pins=(CLK, MOSI, MISO))
.. method:: SPI.init(baudrate=1000000, \*, polarity=0, phase=0, bits=8, firstbit=SPI.MSB, pins=(CLK, MOSI, MISO), sck=None, mosi=None, miso=None)
Initialise the SPI bus with the given parameters:
- ``mode`` must be ``SPI.MASTER``.
- ``baudrate`` is the SCK clock rate.
- ``polarity`` can be 0 or 1, and is the level the idle clock line sits at.
- ``phase`` can be 0 or 1 to sample data on the first or second clock edge
respectively.
- ``bits`` is the width of each transfer, accepted values are 8, 16 and 32.
- ``firstbit`` can be ``SPI.MSB`` only.
- ``pins`` is an optional tuple with the pins to assign to the SPI bus.
- ``bits`` is the width in bits of each transfer. Only 8 of is guaranteed to be supported by all hardware.
- ``firstbit`` can be ``SPI.MSB`` or ``SPI.LSB``.
- ``pins`` is an optional tuple with the pins to assign to the SPI bus (deprecated, only for WiPy).
- ``sck``, ``mosi``, ``miso`` are pins (machine.Pin) objects to use for bus signals. For most
hardware SPI blocks (as selected by ``id`` parameter to the constructore), pins are fixed
and cannot be changed. In some cases, hardware blocks allow 2-3 alterbative pin sets for
a hardware SPI block. Arbitrary pin assignments are possible only for a bitbanging SPI driver
(``id``=-1).
.. method:: SPI.deinit()
......@@ -71,7 +80,7 @@ Methods
Write from ``write_buf`` and read into ``read_buf``. Both buffers must have the
same length.
Returns the number of bytes written
Returns the number of bytes written.
Constants
---------
......@@ -83,3 +92,7 @@ Constants
.. data:: SPI.MSB
set the first bit to be the most significant bit
.. data:: SPI.LSB
set the first bit to be the least significant bit
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