111 lines
3.9 KiB
ReStructuredText
111 lines
3.9 KiB
ReStructuredText
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
|