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Cables and Connectors

Ethernet Port (RJ45) Pin Guide

The RJ45 Connector

The RJ45 is the rectangular plastic connector you see at the end of an Ethernet cable. Inside it houses eight small metal pins.

Pin Assignments and Functions

Ethernet standards like 10BASE-T, 100BASE-TX and 1000BASE-T use these pins in a Twisted Pair configuration.

  • Pin 1 and 2: Transmit Data Pair (TD+ and TD-) – These carry outgoing data from your device towards the network.
  • Pin 3 and 6: Receive Data Pair (RD+ and RD-) – These handle incoming data from the network to your device.
  • Pin 4, 5, 7 and 8: These pins can have different roles.
  • Gigabit Ethernet and Above: Use all 4 pairs for data transmission for faster speeds.
  • Power over Ethernet (PoE): Might use these pins to deliver power along with data to compatible devices (IP/surveillance cameras for example).
  • Unused: In some simpler setups these pins remain unused.

Color Coding

There are two main wiring standards: T568A and T568B.

Ethernet cables are colored to indicate which standard they follow making it easier to match them with ports.

T568A

  • Pin 1: Green/White
  • Pin 2: Green
  • Pin 3: Orange/White
  • Pin 4: Blue
  • Pin 5: Blue/White
  • Pin 6: Orange
  • Pin 7: Brown/White
  • Pin 8: Brown

T568B Swaps the Orange/Green Pairs

  • Pin 1: Orange/White
  • Pin 2: Orange
  • Pin 3: Green/White
  • Pin 4: Blue
  • Pin 5: Blue/White
  • Pin 6: Green
  • Pin 7: Brown/White
  • Pin 8: Brown

Important Things

Crossover vs. Straight through Cables: A crossover cable swaps the transmit and receive pairs on one end helping devices to talk directly. These used to be common but most modern devices support auto negotiation so they are kind of useless these days.

Damage: Bent or broken pins within the RJ45 connector will cause connectivity issues.

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