Ethernet

Ethernet uses a bus or star topology and supports data transfer rates of 10 Mbps (10-BaseT), 100 Mbps (10/100 Base-T) or 1,000 Mbps (1 Gbps). The Ethernet specification serves as the basis for the IEEE 802.3 standard, which specifies the physical and lower software layers. Ethernet uses the CSMA/CD access method to handle simultaneous demands and is one of the most widely implemented LAN standards. For embedded applications, Ethernet is typically used for remote monitor or control of data and the 10 and 100 Mbps transfer rates are used.

A typical Ethernet system is shown in Figures 1 and 2. The Ethernet controller may be a separate, standalone device, or it may be integrated with the host microcontroller (MCU). The Ethernet controller transmits and receives data from the Ethernet cable and
manages Ethernet protocol. Ethernet controllers are often separated into two pieces, the Media Access Control (MAC) and the
Physical Layer (PHY).

Figure 1: Standalone Ethernet Controller

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Figure 2: Integrated Ethernet System

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Media Access Control (MAC)

The MAC provides addressing and channel access control mechanisms for several terminals or network nodes to communicate within
a multi-point network, typical a local area network (LAN). As part of the channel access control, it provides multiple access protocol that allows for an automatic retransmission when a collision occurs. It also emulates a full-duplex logical communication channel in a multi-point network. This channel may provide unicast, multicast or broadcast communication service.

Physical Layer (PHY)

The PHY provides the means of transmitting raw bits over a physical data link (i.e. twisted pair cable). The PHY module interfaces to a signal transformer, which in turn connects to the RJ-45 Ethernet socket. The host controller receives data from the Ethernet controller
and applies the necessary protocol rules. The host controller also formats outgoing data and places it into the Ethernet controller transmit buffer.