MCP2515 Technical Guide

Hardware Connection and Wiring

Here is a typical wiring diagram for connecting an MCP2515 module to an Arduino Uno. Remember that two 120Ω termination resistors are required at each physical end of the CAN bus.

Software: Sending and Receiving

The following code snippets demonstrate how to send and receive a simple message using the `mcp2515` library.

Initialization and Sending

#include <mcp2515.h>
#include <SPI.h>
#define CAN_INT 2
#define CS_PIN 10
MCP2515 mcp2515(CS_PIN);
void setup() {
  Serial.begin(115200);
  SPI.begin();
  if (mcp2515.reset() != MCP2515::ERROR_OK) {
    Serial.println("Error initializing MCP2515");
    while(1);
  }
  if (mcp2515.setBitrate(CAN_125KBPS) != MCP2515::ERROR_OK) {
    Serial.println("Bitrate setting error");
    while(1);
  }
}
void loop() {
  CanMessage msg;
  msg.id = 0x123;
  msg.data[0] = 0xAA;
  msg.data_length_code = 1;
  mcp2515.sendMessage(&msg);
  Serial.println("Message sent!");
  delay(1000);
}

Receiving a Message

#include <mcp2515.h>
#include <SPI.h>
#define CS_PIN 10
MCP2515 mcp2515(CS_PIN);
void setup() {
  // ... (same as above)
}
void loop() {
  CanMessage msg;
  if (mcp2515.readMessage(&msg) == MCP2515::ERROR_OK) {
    Serial.print("Received message ID: 0x");
    Serial.print(msg.id, HEX);
    Serial.print(", Data: ");
    Serial.println(msg.data[0], HEX);
  }
  delay(10);
}

Function Explanations

mcp2515.reset(): This function initializes the chip to a known state. It's crucial for ensuring the MCP2515 is ready to be configured, acting like a software reboot of the chip's internal logic. This should be the first function called after the constructor.

mcp2515.setBitrate(): This function configures the CAN bus speed. It takes a predefined constant like `CAN_125KBPS` or `CAN_500KBPS` and calculates the correct bit timing register values (CNF1, CNF2, CNF3) to match the target bus speed and the oscillator frequency, ensuring all nodes on the network can communicate reliably.

Polling vs. Interrupts

The `loop()` function in the receiving code uses polling by repeatedly calling `mcp2515.readMessage()`. This is simple but can be inefficient as the MCU spends a lot of time checking for new messages even when there are none. A more efficient method is to use an interrupt-driven approach. By connecting the MCP2515's INT pin to a dedicated MCU interrupt pin, the chip can signal the MCU only when a new message arrives, allowing the MCU to perform other tasks while waiting.