circuitpython/docs/library/pyb.CAN.rst

class CAN -- controller area network communication bus
======================================================

CAN implements the standard CAN communications protocol.  At
the physical level it consists of 2 lines: RX and TX.  Note that
to connect the pyboard to a CAN bus you must use a CAN transceiver
to convert the CAN logic signals from the pyboard to the correct
voltage levels on the bus.

Note that this driver does not yet support filter configuration
(it defaults to a single filter that lets through all messages),
or bus timing configuration (except for setting the prescaler).

Example usage (works without anything connected)::

    from pyb import CAN
    can = pyb.CAN(1, pyb.CAN.LOOPBACK)
    can.send('message!', 123)   # send message to id 123
    can.recv(0)                 # receive message on FIFO 0


Constructors
------------

.. class:: pyb.CAN(bus, ...)

   Construct a CAN object on the given bus.  ``bus`` can be 1-2, or 'YA' or 'YB'.
   With no additional parameters, the CAN 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.
   
   The physical pins of the CAN busses are:
   
     - ``CAN(1)`` is on ``YA``: ``(RX, TX) = (Y3, Y4) = (PB8, PB9)``
     - ``CAN(2)`` is on ``YB``: ``(RX, TX) = (Y5, Y6) = (PB12, PB13)``


Methods
-------

.. method:: can.init(mode, extframe=False, prescaler=100, \*, sjw=1, bs1=6, bs2=8)

   Initialise the CAN bus with the given parameters:
   
     - ``mode`` is one of:  NORMAL, LOOPBACK, SILENT, SILENT_LOOPBACK
     - if ``extframe`` is True then the bus uses extended identifiers in the frames
       (29 bits); otherwise it uses standard 11 bit identifiers
     - ``prescaler`` is used to set the duration of 1 time quanta; the time quanta
       will be the input clock (PCLK1, see :meth:`pyb.freq()`) divided by the prescaler
     - ``sjw`` is the resynchronisation jump width in units of the time quanta;
       it can be 1, 2, 3, 4
     - ``bs1`` defines the location of the sample point in units of the time quanta;
       it can be between 1 and 1024 inclusive
     - ``bs2`` defines the location of the transmit point in units of the time quanta;
       it can be between 1 and 16 inclusive

   The time quanta tq is the basic unit of time for the CAN bus.  tq is the CAN
   prescaler value divided by PCLK1 (the frequency of internal peripheral bus 1);
   see :meth:`pyb.freq()` to determine PCLK1.

   A single bit is made up of the synchronisation segment, which is always 1 tq.
   Then follows bit segment 1, then bit segment 2.  The sample point is after bit
   segment 1 finishes.  The transmit point is after bit segment 2 finishes.
   The baud rate will be 1/bittime, where the bittime is 1 + BS1 + BS2 multiplied
   by the time quanta tq.

   For example, with PCLK1=42MHz, prescaler=100, sjw=1, bs1=6, bs2=8, the value of
   tq is 2.38 microseconds.  The bittime is 35.7 microseconds, and the baudrate
   is 28kHz.

   See page 680 of the STM32F405 datasheet for more details.

.. method:: can.deinit()

   Turn off the CAN bus.

.. method:: can.any(fifo)

   Return ``True`` if any message waiting on the FIFO, else ``False``.

.. method:: can.recv(fifo, \*, timeout=5000)

   Receive data on the bus:
   
     - ``fifo`` is an integer, which is the FIFO to receive on
     - ``timeout`` is the timeout in milliseconds to wait for the receive.
   
   Return value: buffer of data bytes.

.. method:: can.send(send, addr, \*, timeout=5000)

   Send a message on the bus:
   
     - ``send`` is the data to send (an integer to send, or a buffer object).
     - ``addr`` is the address to send to
     - ``timeout`` is the timeout in milliseconds to wait for the send.
   
   Return value: ``None``.


Constants
---------

.. data:: CAN.NORMAL
.. data:: CAN.LOOPBACK
.. data:: CAN.SILENT
.. data:: CAN.SILENT_LOOPBACK

   the mode of the CAN bus