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CAN module

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Jaume Olivé Petrus edited this page Apr 13, 2017 · 23 revisions

About this

This module contains functions for accessing the Controller Area Network (CAN) module.

CAN modules are encoded into a byte and are platform-dependent. For this reason the CAN module defines a numeric constant for each available CAN module.

In ESP32 only one CAN module is available, and it's defined by the constant can.CAN0.

Key concepts

A Controller Area Network (CAN bus) is a vehicle bus standard designed to allow MCUs and devices to communicate with each other in applications without a host computer. It is a message-based protocol, designed originally for multiplex electrical wiring within automobiles, but is also used in many other contexts.

ESP32 Notes

The ESP32 CAN module is based on the SJA100 CAN controller, and needs an external CAN transceiver, such as the VP231.

Proposed connection:

ESP32 VP231 Description
GPIO5 / GPIO12 / GPIO25 D CAN TX
GPIO4 / GPIO14 / GPIO35 R CAN RX

Setup functions

can.setup(id, speed)

Setup the CAN module.

Arguments:

  • id: CAN module identifier, for example can.CAN0.
  • speed: speed for the CAN bus expressed in KBits/s.

Returns: noting, or an exception.

-- Setup CAN at 1000 KBits/s
can.setup(can.CAN0, 1000)

Operation functions

can.send(id, frame id, frame type, len, data)

Send a CAN data frame over the CAN bus.

Arguments:

  • id: CAN module identifier.
  • frame id: frame identifier.
  • frame type: frame type, can be either can.STD for a 11-bit identifier, or can.EXT for a 29-bit identifier.
  • len: length of the frame (maximum of 8 byte according to CAN specs).
  • data: a string with the data to send.

Returns: nothing, or an exception.

-- Setup CAN at 1000 KBits/s
can.setup(can.CAN1, 1000)

-- Send a data frame with standard identifier 100 and contents 1234
can.send(can.CAN0, 100, can.STD, 4, "1234")

frame id, frame type, len, data = can.receive(id)

Receives a CAN data frame from the CAN bus. It's the programmer's responsibility to filter the received frames, because filter capabilities are not currently implemented.

Arguments:

  • id: CAN module identifier.

Returns:

  • frame id: frame identifier.
  • frame type: frame type, can be can.STD, or can.EXT.
  • len: length of the received frame.
  • data: a string with the received frame data.
-- Setup CAN at 1000 KBits/s
can.setup(can.CAN1, 1000)

-- Receive data frame
id, type, len, data = can.recv(can.CAN0)

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