Getting Started

What is CAN bus?

Controller Area Network (CAN) is a serial communication protocol that lets microcontrollers and devices talk to each other without a central host computer. Developed by Bosch in the 1980s, it is now the standard in automotive and heavy vehicle electronics.

Why buses use it

In a MAN Lion's City, dozens of ECUs (Electronic Control Units) share data in real time: the engine tells the instrument cluster the RPM, the EBS reports brake air pressure, the tachograph transmits vehicle speed — all over two wires (CAN_H and CAN_L).

The J1939 standard

Heavy vehicles (buses, trucks) use SAE J1939, an application layer built on top of CAN. It defines:

Element Description
29-bit ID Extended identifier (vs 11-bit basic CAN)
PGN Parameter Group Number — identifies the data type
SA Source Address — address of the sending ECU (0x00–0xFE)
SPN Suspect Parameter Number — each signal within a PGN

Implementation parameters

Parameter Value
Bus speed 250 kbps
ID type Extended (29-bit)
Send cycle 20 ms (50 Hz)
Transceiver MCP2515 + TJA1050
MCP2515 oscillator 8 MHz

Note

0xFF bytes in unused positions are the J1939 default for "parameter not available" (SNA — Specific Not Available).

Hardware setup

Compatible boards

Any Arduino with SPI support works. The CS pin and SPI pins vary by board:

Board SCK MOSI MISO CS (recommended) Notes
Arduino Mega 2560 52 51 50 53 Hardware SPI, most headroom
Arduino Uno 13 11 12 10 5V, limited RAM
Arduino Nano 13 11 12 10 Same as Uno, compact
Arduino Micro 15 16 14 10 5V, USB HID capable
Arduino Leonardo 15 16 14 10 Same as Micro
ESP32 18 23 19 5 3.3V — use level shifter

For ESP32, the MCP2515 runs at 3.3V — do not connect directly to a 5V MCP2515 module without a level shifter.

Required components

Component Recommended model
Microcontroller Any board from the table above
CAN module MCP2515 + TJA1050 breakout board
Bus terminators 2× 120 Ω resistor
Wiring Twisted pair for CAN_H / CAN_L

Wiring — Arduino Mega

Arduino Mega MCP2515 module
5V VCC
GND GND
pin 52 SCK
pin 51 MOSI
pin 50 MISO
pin 53 CS
pin 2 INT (optional)

Wiring — Arduino Uno / Nano

Arduino Uno/Nano MCP2515 module
5V VCC
GND GND
pin 13 SCK
pin 11 MOSI
pin 12 MISO
pin 10 CS
pin 2 INT (optional)

Initialization code

Change SPI_CS_PIN to match your board:

#include <SPI.h>
#include <mcp_can.h>

const int SPI_CS_PIN = 10;  // 53 for Mega, 10 for Uno/Nano
MCP_CAN CAN(SPI_CS_PIN);

void setup() {
    while (CAN_OK != CAN.begin(MCP_ANY, CAN_250KBPS, MCP_8MHZ)) {
        delay(100);
    }
    CAN.setMode(MCP_NORMAL);
}

MCP2515 oscillator

Most MCP2515 modules come with an 8 MHz crystal. Some come with 16 MHz — check the crystal printed on your module and change the parameter accordingly:

Crystal Parameter
8 MHz MCP_8MHZ
16 MHz MCP_16MHZ

Installing the library

Install mcp_can by Cory Fowler from the Arduino IDE library manager, or clone directly:

cd ~/Documents/Arduino/libraries
git clone https://github.com/coryjfowler/MCP_CAN_lib

Important

Always place a 120 Ω resistor between CAN_H and CAN_L at each end of the bus. Without terminators, signal reflections will make the bus unstable.