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Intel 8255x 10/100 Mbps Ethernet Controller Family Open Source Software Developer Manual 5
Adapter and Controller Overview 2
Adapters based on an Intel
®
8255x device support the ANSI/IEEE 802.3u standard for 100BASE-
TX (100 Mbps operation) and 10BASE-T (10 Mbps operation).
2.1 Adapter Block Diagram
The main components of Intel Fast Ethernet adapters are:
• A Fast Ethernet Media Access Controller (MAC), such as the 8255x, is the core component.
The MAC supports the Fast Ethernet ANSI/IEEE 802.3u standard.
• A Physical Layer (PHY) interface device is also required. The 82558, 82559, 82550, and
82551 components have an integrated PHY that supports 100BASE-TX and 10BASE-T.
Adapters based on the 82557 must include an appropriate PHY component for their design.
• A serial EEPROM is required to hold the adapter’s individual Ethernet node address and other
configuration information including fixed PCI configuration parameters.
The adapters are based on 100BASE-TX specifications. 100BASE-TX is a specific scheme
designed for use over 2 pairs of Category 5 unshielded twisted-pair cable. 100BASE-TX defines a
signaling scheme for 100 Mbps and provides compatibility with the existing 10 Mbps IEEE 802.3
10BASE-T signaling standard. Since only 2-wire pairs are used, TX technology allows full duplex
operation at 100 Mbps. The Intel 82555 is one possible TX solution.
The block diagram below illustrates an Intel
®
PRO/100B adapter configuration based on the 82557
MAC with a TX or T4 PHY.
Figure 1. 82557 Network Interface Card Block Diagram
RJ-45
Filter
Module
100BASE-T4 or
100BASE-TX PHY
Intel® 82557
EEPROM
Optional
Flash
PCI Local Bus
MII