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© 2008 Microchip Technology Inc. DS01120A-page 1
AN1120
INTRODUCTION
This document specifies the theory and operation of
the Ethernet technology found in PIC
®
MCUs with
integrated Ethernet and in stand-alone Ethernet
controllers.
Ethernet technology contains acronyms and terms
defined in Table 1.
APPLICATIONS
Ethernet is an asynchronous Carrier Sense Multiple
Access with Collision Detect (CSMA/CD)
protocol/interface, with a payload size of 46-1500 octets.
With data rates of tens to hundreds of megabits/second,
it is generally not well suited for low-power applications.
However, with ubiquitous deployment, internet
connectivity, high data rates and limitless range
expansibility, Ethernet can accommodate nearly all
wired communications requirements. Potential
applications include:
• Remote sensing and monitoring
• Remote command, control and firmware updating
• Bulk data transfer
• Live streaming audio, video and media
• Public data acquisition (date/time, stock quotes,
news releases, etc.)
THEORY OF OPERATION
Ethernet is a data link and physical layer protocol
defined by the IEEE 802.3™ specification. It comes in
many flavors, defined by maximum bit rate, mode of
transmission and physical transmission medium.
• Maximum Bit Rate (Mbits/s): 10, 100, 1000, etc.
• Mode of Transmission: Broadband, Baseband
• Physical Transmission Medium: Coax, Fiber, UTP, etc.
Author: M. Simmons
Microchip Technology Inc.
TABLE 1: ETHERNET GLOSSARY
Term Definition
CRC Cyclic Redundancy Check: Type of checksum algorithm used when computing the FCS for all
Ethernet frames and the hash table key for hash table filtering of receive packets.
DA Destination Address: The 6-octet destination address field of an Ethernet frame.
ESD End-of-Stream Delimiter: In 100 Mb/s operation, the ESD is transmitted after the FCS (during
the inter-frame gap) to denote the end of the frame.
FCS Frame Check Sequence: The 4-octet field at the end of an Ethernet frame that holds the error
detection checksum for that frame.
IP Internet Protocol: Refers either to IPv4 or IPv6.
LAN Local Area Network or Large Area Network.
MAC Media Access Control: The block responsible for implementing the Media Access Control
functions of the Ethernet specification.
MAC Address A 6-octet number representing the physical address of the node(s) on an Ethernet network.
Every Ethernet frame contains both a source and destination address, both of which are MAC
addresses.
MDI Medium Dependent Interface or Management Data Input.
MDO Management Data Output.
MDIO Management Data Input/Output.
MII Media Independent Interface: Standard 4-bit interface between the MAC and the PHY for
communicating TX and RX frame data. In 10 Mb/s mode, the MII runs at 2.5 MHz; in
100 Mb/s mode, it runs at 25 MHz.
MIIM MII Management: Set of MII sideband signals used for accessing the PHY registers.
Ethernet Theory of Operation
