Ethernet: 10/100/1000Base-T Ethernet Port Pinouts

This document provides the pinouts for the 10/100 and Gigabit Ethernet ports on Macintosh computers.
This article has been archived and is no longer updated by Apple.
This article is relevant for the following products:
  • iMac
  • Power Mac G4
  • PowerBook G3 Series (Bronze Keyboard)
  • PowerBook (FireWire)
  • PowerBook G4
  • iBook (FireWire)
  • iBook (Dual USB)
  • Macintosh Server G3
  • Power Macintosh G3 (Blue and White)

An Ethernet port uses an RJ-45 connector. It is typically located on the back or side of the computer. Table 1 shows the signals and pin assignments for 10Base-T and 100Base-T. Table 2 shows the signals and pin assignments for 1000Base-T, otherwise known as gigabit Ethernet.

Table 1 Signals for 10Base-T and 100Base-T

Pin Signal nameSignal definition
1TXP Transmit (positive lead)
2TXN Transmit (negative lead)
3RXP Receive (positive lead)
4­Not used
5­Not used
6RXN Receive (negative lead)
7 ­Not used
8 ­Not used

Table 2 Signals for 1000Base-T
Pin Signal nameSignal definition
1TRD+(0) Transmit and receive data 0 (positive lead)
2TRD­(0) Transmit and receive data 0 (negative lead)
3TRD+(1) Transmit and receive data 1 (positive lead)
4TRD+(2)Transmit and receive data 2 (positive lead)
5TRD­(2)Transmit and receive data 2 (negative lead)
6TRD­(1) Transmit and receive data 1 (negative lead)
7TRD+(3)Transmit and receive data 3 (positive lead)
8TRD­(3)Transmit and receive data 3 (negative lead)

Gigabit Ethernet is a standard developed by the Gigabit Ethernet Alliance, and defined by the IEEE 802.3 committee. The aim of this standard is to utilize existing local area network infrastructure to achieve up to 1 gigabit per second (1 Gbps) transfer rates. This is why gigabit Ethernet utilizes Category 5 or better unshielded twisted pair cabling (UTP), and the RJ-45 connector that is used in 10/100 megabits per second (Mbps) networks. To achieve maximum transfer rates from gigabit Ethernet capable hardware, you also need to install gigabit Ethernet compliant switches, hubs, and routers. Otherwise, the computer switches to a 10 Mbps or 100 Mbps transfer rate depending upon the network hardware that is used.

To utilize gigabit Ethernet, you must use an Ethernet cable with all eight wires (four pairs) present. If you use an inexpensive two pairs-wired cable, the maximum connection speed can only be 100 Mbps.

The Ethernet interface conforms to the ISO/IEC 802.3 specification, where applicable, and complies with IEEE specifications 802.3i (10Base-T), 802.3u-1995 (100Base-T), and 802.3ab (1000Base-T).

Published Date: Oct 7, 2016