Gigabit Ethernet

Owned by lwbantot@uwaterloo.ca (Deactivated)
Last updated: Apr 03, 2021 by c2bains@uwaterloo.ca (Deactivated)
2 min read

Gigabit Ethernet is a transmission technology that is used to network devices in a wired local environment. This environment is called a Local Area Network (LAN) and allows connected devices to send and receive data over a cable at a rate of 1 billion bits per second. The main components include the RJ45 connector that connects to the ethernet cable, the 4 differential pairs that transmit data, and the controller that acts as a bridge between the ethernet and the PCIe or RGMII microcontrollers.

Resources:

https://resources.altium.com/p/gigabit-ethernet-101-basics-implementation


RJ45 Connector & Magnetics

The RJ45 connector is the standard to connect to an ethernet cable with 8 pins that correspond to 4 bi-directional differential pairs. In gigabit ethernet, all 4 differential pairs are used, and a minimum of Category 5 cable is required. Magnetic Transformers are required for these differential pairs to isolate the communication wires from the rest of the system and ensure that their signal isn’t corrupted by any faults elsewhere. They can either be integrated with the RJ45 connector or added externally in the schematic design. 

Resources:
https://www.avnet.com/wps/portal/abacus/resources/article/ethernet-magnetics-discrete-or-integrated/

https://networkengineering.stackexchange.com/questions/29927/what-is-the-purpose-of-an-ethernet-magnetic-transformer-and-how-are-they-used


4 Transmit and Receive Differential Pairs

Gigabit Ethernet uses 4 differential pairs to transmit and receive data. Each of these pairs is bi-directional so they can send and receive data at the same time. They are also backwards compatible with slower methods of ethernet such as 100 Mbps and 10Mbps. The naming and colour codes for these pairs are seen below:

The data is sent in 56-bit packages with the following structure:

Resources:
http://www.interfacebus.com/Gigabit_Ethernet_Description.html

https://allpinouts.org/pinouts/connectors/networking/ethernet-1000base-t-gigabit/


Controller

The ethernet controller is the bridge between the ethernet and the microcontroller that uses either PCIe or RGMII for further data transmission. They use an external oscillator as a reference clock to transmit data to PCIe/RGMII. It is also common to use an EEPROM for non-volatile data storage and to program the GPIO pins.


Resources:
https://ww1.microchip.com/downloads/en/DeviceDoc/LAN7430-LAN7431-Data-Sheet-DS00002631D.pdf