MCP2515 CAN Controller Library for Arduino

Compatibility with the ACAN library

This library is fully compatible with the Teensy 3.x ACAN library https://github.com/pierremolinaro/acan, it uses a very similar API and the same CANMessage class for handling messages.

ACAN2515 library description

ACAN2515 is a driver for the MCP2515 CAN Controller. It runs on any Arduino compatible board.

You can choose any frequency for your MCP2515, the actual frequency is a parameter of the library.

The driver supports many bit rates: for a 16 MHz quartz, the CAN bit timing calculator finds settings for standard 62.5 kbit/s, 125 kbit/s, 250 kbit/s, 500 kbit/s, 1 Mbit/s, but also for an exotic bit rate as 727 kbit/s. If the desired bit rate cannot be achieved, the begin method does not configure the hardware and returns an error code.

Driver API is fully described by the PDF file in the extras directory.

Demo Sketch

The demo sketch is in the examples/LoopBackDemo directory.

Configuration is a four-step operation.

1. Instanciation of the settings object : the constructor has one parameter: the wished CAN bit rate. The settings is fully initialized.
2. You can override default settings. Here, we set the mRequestedMode property to true, enabling to run demo code without any additional hardware (no CAN transceiver needed). We can also for example change the receive buffer size by setting the mReceiveBufferSize property.
3. Calling the begin method configures the driver and starts CAN bus participation. Any message can be sent, any frame on the bus is received. No default filter to provide.
4. You check the errorCode value to detect configuration error(s).

static const byte MCP2515_CS  = 20 ; // CS input of MCP2515, adapt to your design
static const byte MCP2515_INT = 37 ; // INT output of MCP2515, adapt to your design

ACAN2515 can (MCP2515_CS, SPI, MCP2515_INT) ; // You can use SPI2, SPI3, if provided by your microcontroller

const uint32_t QUARTZ_FREQUENCY = 16 * 1000 * 1000 ; // 16 MHz

void setup () {
  Serial.begin (9600) ;
  while (!Serial) {}
  Serial.println ("Hello") ;
  ACAN2515Settings settings (QUARTZ_FREQUENCY, 125 * 1000) ; // 125 kbit/s
  settings.mRequestedMode = ACAN2515Settings::LoopBackMode ; // Select loopback mode
  const uint16_t errorCode = can.begin (settings, [] { can.isr () ; }) ;
  if (0 == errorCode) {
    Serial.println ("Can ok") ;
  }else{
    Serial.print ("Error Can: 0x") ;
    Serial.println (errorCode, HEX) ;
  }
}

Now, an example of the loop function. As we have selected loop back mode, every sent frame is received.

static uint32_t gSendDate = 0 ;
static uint32_t gSentCount = 0 ;
static uint32_t gReceivedCount = 0 ;

void loop () {
  CANMessage message ;
  if (gSendDate < millis ()) {
    message.id = 0x542 ;
    const bool ok = can.tryToSend (message) ;
    if (ok) {
      gSendDate += 2000 ;
      gSentCount += 1 ;
      Serial.print ("Sent: ") ;
      Serial.println (gSentCount) ;
    }
  }
  if (can.receive (message)) {
    gReceivedCount += 1 ;
    Serial.print ("Received: ") ;
    Serial.println (gReceivedCount) ;
  }
}

CANMessage is the class that defines a CAN message. The message object is fully initialized by the default constructor. Here, we set the id to 0x542 for sending a standard data frame, without data, with this identifier.

The can.tryToSend tries to send the message. It returns true if the message has been sucessfully added to the driver transmit buffer.

The gSendDate variable handles sending a CAN message every 2000 ms.

can.receive returns true if a message has been received, and assigned to the messageargument.

Use of Optional Reception Filtering

The MCP2515 CAN Controller implements two acceptance masks and six acceptance filters. The driver API enables you to fully manage these registers.

For example (loopbackUsingFilters sketch):

  ACAN2515Settings settings (QUARTZ_FREQUENCY, 125 * 1000) ;
  settings.mRequestedMode = ACAN2515Settings::LoopBackMode ; // Select loopback mode
  const ACAN2515Mask rxm0 = extended2515Mask (0x1FFFFFFF) ; // For filter #0 and #1
  const ACAN2515Mask rxm1 = standard2515Mask (0x7F0, 0xFF, 0) ; // For filter #2 to #5
  const ACAN2515AcceptanceFilter filters [] = {
    {extended2515Filter (0x12345678), receive0},
    {extended2515Filter (0x18765432), receive1},
    {standard2515Filter (0x560, 0x55, 0), receive2}
  } ;
  const uint16_t errorCode = can.begin (settings, [] { can.isr () ; }, rxm0, rxm1, filters, 3) ;

These settings enable the acceptance of extended frames whose identifier is 0x12345678 or 0x18765432, and data frames whose identifier is 0x560 and first data byte, if any, is 0x55.

The receive0, receive1, receive2 functions are call back functions, handled by the can.dispatchReceivedMessage function:

void loop () {
  can.dispatchReceivedMessage () ; // Do not use can.receive any more
  ...
}