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Diffstat (limited to 'docs/library/machine.SPI.rst')
| -rw-r--r-- | docs/library/machine.SPI.rst | 81 |
1 files changed, 52 insertions, 29 deletions
diff --git a/docs/library/machine.SPI.rst b/docs/library/machine.SPI.rst index 73b3a3996d..dda6314fa2 100644 --- a/docs/library/machine.SPI.rst +++ b/docs/library/machine.SPI.rst @@ -1,10 +1,14 @@ .. currentmodule:: machine -class SPI -- a master-driven serial protocol -============================================ +class SPI -- a Serial Peripheral Interface bus protocol (master side) +===================================================================== -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 synchronous serial protocol that is driven by a master. At the +physical level, a bus consists 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 @@ -21,65 +25,84 @@ 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, sck=None, mosi=None, miso=None, pins=(SCK, MOSI, MISO)) 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 is guaranteed to be supported by all hardware. + - ``firstbit`` can be ``SPI.MSB`` or ``SPI.LSB``. + - ``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 alternative pin sets for + a hardware SPI block. Arbitrary pin assignments are possible only for a bitbanging SPI driver + (``id`` = -1). + - ``pins`` - WiPy port doesn't ``sck``, ``mosi``, ``miso`` arguments, and instead allows to + specify them as a tuple of ``pins`` paramter. .. method:: SPI.deinit() Turn off the SPI bus. -.. method:: SPI.write(buf) +.. method:: SPI.read(nbytes, write=0x00) + + Read a number of bytes specified by ``nbytes`` while continuously writing + the single byte given by ``write``. + Returns a ``bytes`` object with the data that was read. + +.. method:: SPI.readinto(buf, write=0x00) - Write the data contained in ``buf``. - Returns the number of bytes written. + Read into the buffer specified by ``buf`` while continuously writing the + single byte given by ``write``. + Returns ``None``. -.. method:: SPI.read(nbytes, *, write=0x00) + Note: on WiPy this function returns the number of bytes read. - Read the ``nbytes`` while writing the data specified by ``write``. - Return the number of bytes read. +.. method:: SPI.write(buf) -.. method:: SPI.readinto(buf, *, write=0x00) + Write the bytes contained in ``buf``. + Returns ``None``. - Read into the buffer specified by ``buf`` while writing the data specified by - ``write``. - Return the number of bytes read. + Note: on WiPy this function returns the number of bytes written. .. method:: SPI.write_readinto(write_buf, read_buf) - Write from ``write_buf`` and read into ``read_buf``. Both buffers must have the + Write the bytes from ``write_buf`` while reading into ``read_buf``. The + buffers can be the same or different, but both buffers must have the same length. - Returns the number of bytes written + Returns ``None``. + + Note: on WiPy this function returns the number of bytes written. Constants --------- .. data:: SPI.MASTER - for initialising the SPI bus to master + for initialising the SPI bus to master; this is only used for the WiPy .. 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 |