How many volts are CAN high and CAN low in a car?

CAN (Controller Area Network) is a communication protocol used in automotive and other industrial applications. The CAN bus uses a pair of twisted wires (CANH and CANL) to transmit data, where CANH is often referred to as "CAN high" and CANL is referred to as "CAN low".

1. CAN bus voltage overview

The CAN bus is a differential signal transmission method, and its voltage level depends on the voltage difference between CANH and CANL. In CAN communication, the voltage difference determines the logic state of the signal. Usually, the CAN bus voltage is divided into two logic states: logic 0 (dominant) and logic 1 (recessive).

1. CAN bus voltage standard

There are two voltage standards for the CAN bus: CAN 2.0A and CAN 2.0B. The two standards differ in voltage levels.

2.1 CAN 2.0A

The CAN 2.0A standard specifies two voltage ranges: High-Speed ​​CAN (HSC) and Low-Speed ​​CAN (LSC).

• High-Speed ​​CAN (HSC): CANH is between 2.5V and 5V, CANL is between 0V and 1.5V.

• Low-Speed ​​CAN (LSC): CANH is between 2.5V and 5V, CANL is between 0V and 0.5V.

2.2 CAN 2.0B

The CAN 2.0B standard specifies a voltage range that applies to all CAN communications.

• CAN 2.0B: CANH is between 2.5V and 5V, CANL is between 0V and 0.5V.

1. CAN bus voltage logic state

In CAN bus communication, the voltage difference between logic 0 (dominant) and logic 1 (recessive) determines the transmission of data.

3.1 Logic 0 (dominant)

When CANH is lower than CANL, it indicates a logic 0 (dominant). In this case, the voltage range of CANH is usually between 0V and 0.5V, while the voltage range of CANL is between 2.5V and 5V.

3.2 Logic 1 (implicit)

When CANH is higher than CANL, it indicates a logical 1 (recessive). In this case, the voltage range of CANH is usually between 3.5V and 5V, while the voltage range of CANL is between 0V and 0.5V.

1. CAN bus voltage stability

In order to ensure the stability of CAN bus communication, it is necessary to ensure that the voltage difference between CANH and CANL remains within a certain range. This is usually achieved by using terminal resistors. Terminal resistors are usually connected at both ends of CANH and CANL to reduce signal reflection and improve signal quality.

1. CAN bus voltage anti-interference ability

The CAN bus has strong anti-interference ability, which is mainly due to its differential signal transmission method. Differential signal transmission can effectively resist external electromagnetic interference and improve communication reliability.

1. CAN bus voltage and communication rate

The communication rate (baud rate) of the CAN bus is related to the voltage level. In high-speed CAN communication, the voltage difference is large and the signal transmission speed is fast. In low-speed CAN communication, the voltage difference is small and the signal transmission speed is slow.

1. CAN bus voltage and power supply

The power supply of CAN bus is usually 5V or 12V. In practical applications, it is necessary to select a suitable power supply according to the requirements of CAN bus equipment. At the same time, it is also necessary to consider the stability and anti-interference ability of the power supply to ensure the reliability of CAN bus communication.

1. CAN bus voltage measurement and debugging

During the debugging of the CAN bus system, it is necessary to measure the voltage difference between CANH and CANL to ensure normal communication. Tools such as oscilloscopes or logic analyzers can be used to measure the CAN bus voltage and adjust system parameters based on the measurement results.

1. CAN bus voltage fault diagnosis

When there is a problem with CAN bus communication, it may be related to voltage. For example, a voltage difference that is too small may cause signal instability, while a voltage difference that is too large may cause equipment damage. Therefore, during the fault diagnosis process, it is necessary to check the voltage difference between CANH and CANL and adjust it as needed.

1. in conclusion

CAN bus is a communication protocol widely used in automobiles and other industrial fields. Its voltage level is crucial to the stability and reliability of communication. Understanding the voltage standards, logic states, stability, anti-interference capabilities of CAN high and CAN low will help to better design, debug and maintain CAN bus systems in practical applications.