MAN CAN BUS

• Getting Started
• What is CAN bus?
• Hardware setup
• Message Overview

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:

Implementation parameters

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:

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

Required components

Wiring — Arduino Mega

Wiring — Arduino Uno / Nano

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:

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.

Message Overview

This implementation sends 6 messages every 20 ms (50 Hz cycle). All use 29-bit extended IDs and 8 data bytes, conforming to SAE J1939.

Message table

29-bit ID structure

Every J1939 message ID encodes three fields:

Byte convention

Unused bytes are always set to 0xFF, which in J1939 means parameter not available (SNA — Specific Not Available).

Byte:   0     1     2     3     4     5     6     7
      ┌─────┬─────┬─────┬─────┬─────┬─────┬─────┬─────┐
      │ FF  │ FF  │ FF  │ Lo  │ Hi  │ FF  │ FF  │ FF  │
      └─────┴─────┴─────┴─────┴─────┴─────┴─────┴─────┘
                          ↑     ↑
                    Actual data (little-endian)

Send cycle

All 6 messages are sent sequentially every 20 ms:

void loop() {
    // send all messages
    // ...
    delay(20);  // 50 Hz
}

Source addresses in use