CAN and RS485 are commonly used serial communication protocols, and they are widely used in many industrial control, automation, and robotics fields. These two communication protocols are recommended to use twisted-pair wires to transmit signals. In this paper, we will discuss why CAN and RS485 are recommended to use twisted-pair wires from both theoretical and practical aspects, and introduce the advantages and applications of twisted-pair wires.
I. Theoretical principles
1, anti-interference ability
CAN and RS485 are both serial communication protocols, which need to be realized through transmission lines when transmitting signals. Due to the existence of a large number of interference sources around the transmission line, such as electromagnetic waves, power supply noise, electrical interference, etc., these sources of interference will adversely affect the signal transmission, resulting in signal distortion, BER and other problems.
Twisted-pair cable consists of two wires twisted together, its twisted structure can effectively reduce the impact of the surrounding interference on the signal, each wire in the transmission of the waves radiated by the other wire will be canceled out by the waves emitted on the other wire, thus improving the signal's anti-jamming ability.
2,Impedance Matching
Impedance matching is a very important issue in signal transmission. If the impedance of the transmission line is not matched, it will lead to problems such as reflection, foldback and distortion of the signal. The above figure also shows the impedance mismatch of CAN bus.
The impedance matching performance of twisted pair cable is very good, which can effectively avoid problems such as signal reflection and foldback.
3,Capacitance and inductance
The capacitance and inductance of a transmission line are important factors that affect the quality of signal transmission. The capacitance of the transmission line causes delay and distortion of the signal, while the inductance reduces the bandwidth of the signal and increases the attenuation of the signal. The stranded structure of twisted pair can effectively reduce the capacitance and inductance of the transmission line, thus improving the quality and speed of signal transmission.
II. the practice of application
1,CAN bus application
CAN bus is a communication protocol widely used in industrial control and automotive electronics and other fields. In CAN bus, the two communicating parties communicate through two twisted pairs of wires. Since the CAN bus usually works in a harsh environment with a lot of electromagnetic interference and noise, CAN bus needs to use twisted-pair wires to improve the stability and reliability of signal transmission.
2,RS485 application
RS485 is a communication protocol widely used in automation control, data acquisition and robotics and other fields. RS485 communication protocol can support multi-point communication and long-distance transmission, so in some occasions that require long-distance data transmission, RS485 is also a very good choice.
The main reason for RS485 to use twisted pair is to improve the anti-interference ability of the signal and reduce the impedance of the transmission line, so as to realize longer distance transmission and more stable and reliable communication.
In addition to CAN and RS485, twisted-pair cables are widely used in Ethernet, telephone lines, television lines and audio lines. Ethernet is a local area network communication protocol, and the commonly used Ethernet cable is also a twisted pair cable, which has the advantages of high-speed transmission, strong anti-interference ability and stability and reliability, and is suitable for occasions that require high-speed transmission and stable communication. Telephone and TV cables are also twisted-pair cables, and the use of twisted-pair cables can improve the quality and distance of signal transmission, thus realizing better communication effects. Audio cable is also often used twisted pair, can effectively reduce the electromagnetic interference and noise on the audio signal, thus improving the quality of audio signals.
Summarize
Twisted-pair cable is an excellent transmission line, which has excellent performance in terms of anti-interference capability, impedance matching and capacitance inductance. In CAN, RS485 and other communication protocols, the use of twisted-pair wires can improve the quality and reliability of signal transmission, resulting in more stable and reliable communication. In practical applications, suitable twisted-pair cables should be selected according to actual needs and environmental requirements, and appropriate cabling and wiring measures should be taken to ensure the best performance and effect of twisted-pair cables.