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.
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Resources:
https://resources.altium.com/p/gigabit-ethernet-101-basics-implementation
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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. , and therefore 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
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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