In the communication systems of modern industrial automation and robotics, bus technology plays a vital role. Whether it is CAN bus, RS485 or other high-speed digital communication systems, terminal resistors are key components to ensure the quality of signal transmission. Next, we will explore in depth the working principle, configuration method and specific application of terminal resistors in various bus systems.
1. Basic principles of terminal resistance
When an electrical signal propagates on a transmission line, if the characteristic impedance of the transmission line does not match the load impedance, signal reflection will occur. This reflection will cause signal waveform distortion, manifested as signal overshoot, ringing, and edge degradation.
The main function of the terminal resistor is to achieve impedance matching, which is specifically manifested as follows:
1) Eliminate signal reflection: match the cable characteristic impedance (usually 120Ω)
2) Improve signal quality: reduce ringing and overshoot
3) Enhance anti-interference ability: reduce the impact of common mode noise
4) Stable bus level: ensure correct logic level recognition
2. Application of terminal resistors in common bus systems
A. CAN bus system
In the CAN bus (ISO 11898), the terminal resistor configuration has strict specifications:
Standard value: 120Ω (corresponding to cable characteristic impedance)
Configuration location: nodes at both physical ends of the bus
B. RS-485 Network
The RS-485 bus has different requirements for terminal resistance:
Matching resistance: equal to the cable characteristic impedance (usually 120Ω)
Bias resistor: Additional required (typical value 560Ω)
Configuration principles:
a. Install terminal resistors only at both ends of the line
b. Relay nodes should not add terminals
3. Typical fault phenomena
a. Signal oscillation:
Possible cause: Terminal resistance missing
Solution: Check the terminals at both ends
b. Shortened communication distance:
Possible cause: The terminal resistance value is wrong
Solution: Measure the actual resistance
c. Abnormal bus load:
Possible cause: Excess terminal resistance
Solution: Remove the intermediate node terminal
Although the terminal resistor seems to be a simple component in the bus system, it is actually the key to ensure communication reliability. Correct terminal resistor configuration can:
1) Improve signal integrity
2) Extend the communication distance
3) Enhance system stability
As bus rates continue to increase, terminal technology will continue to evolve, but the basic principle of impedance matching will always be the golden rule for high-speed digital communication design. The servo drive developed by Shenzhen Zhongling Technology can control wheel hub motors, servo motors, etc., and is widely used in industries such as robots. It supports CANOPEN and RS485 bus control and is equipped with terminal resistors, which provides a basis for ensuring signal integrity under high-speed digital communication.
Post time: Jul-08-2025