Overview of CAN Bus

The CAN bus is similar to the RS485 bus in that both use differential signal lines for transmission. The two signal lines in CAN are CAN_H and CAN_L, which have equal signal amplitudes but opposite phases. The voltage difference between these two lines represents logic levels:

• A positive voltage difference indicates logic 0.
• A zero (or negative) voltage difference indicates logic 1.

Typical CAN Bus Implementation

A CAN bus system typically consists of:

• MCU (Microcontroller Unit)
• CAN controller
• CAN transceiver

CAN Bus Standards

The CAN bus has evolved into two international standards: ISO11519 and ISO11898. Their key differences are as follows:

1. ISO11898 (High-Speed, Short-Distance Closed-Loop Network):
   • Maximum bus length: 40 meters
   • Maximum communication speed: 1 Mbps
   • Requires a 120-ohm termination resistor at each end of the bus.

2. ISO11519-2 (Low-Speed, Long-Distance Open-Loop Network):
   • Maximum transmission distance: 1 km
   • Maximum communication speed: 125 kbps
   • Each bus line requires a 2.2 kΩ series resistor. The two lines are independent and do not form a closed loop.

Practical Design Considerations

When designing a CAN bus system, the wiring method depends on the characteristics of the MCU’s CAN controller. For example, the STM32F103 microcontroller has the following CAN controller features:

• Supports CAN2.0A and CAN2.0B protocols.
• Communication speed up to 1 Mbps.
• Classified as a high-speed bus.

Conclusion

The CAN bus is a robust and reliable communication protocol widely used in automotive and industrial applications. Its design requires careful consideration of the specific standard (ISO11898 or ISO11519) and the characteristics of the MCU and transceiver components. In the next installment, we will focus on analyzing the details of the CAN protocol itself.