CAN Shield
==========

The CAN Shield gives the OpenMV Cam a CAN-bus link via a DB9 connector, with an on-board 12 V to 5 V regulator so the shield can power the camera from a vehicle bus.

.. image:: ../can-shield-hero.jpg
    :alt: CAN Shield
    :width: 400px
    :align: center

For full datasheet, photos, and ordering see the
`CAN Shield product page <https://openmv.io/products/can-shield>`_.

.. note::

   Not supported on the OpenMV Cam RT1062.

Highlights
----------

* CAN bus up to 1 Mb/s
* On-board 12 V to 5 V regulator

Pinout
------

.. image:: ../pinout-can-shield.png
    :alt: CAN Shield Pinout
    :width: 700px

Pin reference
-------------

.. csv-table::
   :header: "Pin", "Function"
   :widths: 20, 80

   "P2",        "CAN TX"
   "P3",        "CAN RX"
   "P6",        "CAN standby (optional — see note)"
   "PWR in",    "12 V vehicle-bus input on the DB9 connector"
   "VIN out",   "5 V regulator output (powers the camera)"
   "3.3V rail", "Powers the SN65HVD230 logic"
   "GND rail",  "Common ground"

.. note::

   The SN65HVD230's standby line is disconnected from P6 by default.
   Connect the on-board solder bridge to tie it to P6, then drive P6
   high to put the transceiver into listen-only standby mode (low
   keeps it in normal transmit-and-receive mode).

.. note::

   CANL, CANH, VIN, and GND from the DB9 connector are also broken
   out to through-hole pads on the bottom of the shield — solder
   wires there if you want to skip the DB9 entirely.

.. note::

   The DB9 pinout can be changed between the standard DB9 CAN layout
   and the OBD-II layout by changing the three solder-bridge jumpers
   on the bottom of the shield.

.. note::

   The on-board 120-ohm termination resistor is connected by default.
   It can be disabled via a solder bridge on the bottom of the shield
   for buses that already have termination elsewhere.

Usage
-----

.. note::

   The ``CAN(1)`` peripheral number below follows the STM32 mapping.
   On another processor the bus wired to these pins may be different
   — check your board's reference.

Send and receive frames on the CAN bus at 1 Mb/s::

    from machine import CAN
    import time

    can = CAN(1, 1_000_000)

    can.send([0xDE, 0xAD, 0xBE, 0xEF], 0x123)
    print(can.recv())

With the on-board solder bridge connected, drive P6 high to put the
SN65HVD230 into listen-only standby mode (low returns it to normal
transmit-and-receive)::

    from machine import Pin
    Pin("P6", Pin.OUT).value(1)  # listen-only standby