Basic knowledge of RJ45 interface

RJ45 interface is usually used for data transmission, and the most common application is the network card interface. The RJ-45 port is our most common port. It is our common twisted pair Ethernet port, because twisted pair is mainly used as the transmission medium in Fast Ethernet.

The RJ45 type network cable plug, also known as the crystal plug, is made of eight cores and is widely used in LAN and ADSL broadband Internet users to connect network cables (called Category 5 cables or twisted pairs) between network devices. There are two kinds of colors, one is orange and white, orange, green and white, blue, blue and white, green, brown and white, and brown; the other is green and white, green, orange and white, blue, blue and white, orange, brown and white, Brown; therefore, there are two types of lines using RJ45 connectors: straight-through lines and crossover lines. They are called T568A line sequence and T568B line sequence respectively.

2. RJ45 T568A and T568B usage scenarios

T568A line sequence is suitable for cross interconnection situations. The so-called crossover means that one end of the network cable and the other end are wired differently from the RJ45 network cable plug. One end follows the T568A line sequence, and the other end follows the T568B line sequence. The usage scenarios include

（1）. Computer------Computer

（2）. Hub--------hub

（3）. Switch----switch

The corresponding relationship between the pins of the RJ45 type network cable plug and the network cable color mark is: plug pin number network cable color 1 green white 2 green 3 orange white 4 blue 5 blue white 6 orange 7 brown white 8 brown.

Applicable scope of T568B line sequence

Directly connected to the Internet, both ends of the network cable are not T568B

（1）. Computer-------ADSL cat

（2）. Computer ------- hub or switch

 Cross-connection, one end of the network cable is connected according to T568B, and the other end is connected according to T568A.

（1）. Hub ------- Hub

（2）. Switch ------- switch

The corresponding relationship between the pins of the RJ45 type network cable plug and the network cable color mark is: plug pin number network cable color 1 orange white 2 orange 3 green white 4 blue 5 blue white 6 green 7 brown white 8 brown.

3. Type of RI45 interface

RJ45 interfaces are commonly used for Ethernet interfaces and support 10M and 100M adaptive network switching speeds. There are two common types of RJ45 interfaces. There are DTE types used for interface types such as Ethernet network cards and routers, and there are DCE types used for switches, etc. When two devices are connected using RJ45 communication, a crossover cable must be used.

       Pin information table

4. Precautions when using RJ45

When using the RJ45 socket connector, do not use excessive force when connecting to the RJ45. This may cause damage to the spring blades in the RJ45 socket, resulting in unstable connection.

The RJ45 plug connector has many pins. During the installation process, the pins must be in order and the contact points must be connected. Otherwise, some poor contacts may occur, which may seriously lead to failure to work.

The RJ45 socket connector interface is made of metal inside. Be careful not to get damp or come into contact with water, otherwise it will cause a short circuit.