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Introduction
713
SPRUH82C – April 2013 – Revised September 2016
Copyright © 2013–2016, Texas Instruments Incorporated
EMAC/MDIO Module
18.1.4 Industry Standard(s) Compliance Statement
The EMAC peripheral conforms to the IEEE 802.3 standard, describing the Carrier Sense Multiple Access
with Collision Detection (CSMA/CD) Access Method and Physical Layer specifications. The IEEE 802.3
standard has also been adopted by ISO/IEC and re-designated as ISO/IEC 8802-3:2000(E).
However, the EMAC deviates from the standard in the way it handles transmit underflow errors. The
EMAC MII interface does not use the Transmit Coding Error signal MTXER. Instead of driving the error pin
when an underflow condition occurs on a transmitted frame, the EMAC intentionally generates an incorrect
checksum by inverting the frame CRC, so that the transmitted frame is detected as an error by the
network.
18.1.5 Terminology
The following is a brief explanation of some terms used in this chapter.
Term
Meaning
Broadcast MAC
Address
A special Ethernet MAC address used to send data to all Ethernet devices on the
local network. The broadcast address is FFh-FFh-FFh-FFh-FFh-FFh. The LSB of
the first byte is odd, qualifying it as a group address; however, its value is reserved
for broadcast. It is classified separately by the EMAC.
Descriptor (Packet
Buffer Descriptor)
A small memory structure that describes a larger block of memory in terms of size,
location, and state. Descriptors are used by the EMAC and application to describe
the memory buffers that hold Ethernet data.
Device
In this chapter, device refers to the processor.
Ethernet MAC
Address (MAC
Address)
A unique 6-byte address that identifies an Ethernet device on the network. In an
Ethernet packet, a MAC address is used twice, first to identify the packet’s
destination, and second to identify the packet’s sender or source. An Ethernet MAC
address is normally specified in hexadecimal, using dashes to separate bytes. For
example, 08h-00h-28h-32h-17h-42h.
The first three bytes normally designate the manufacturer of the device. However,
when the first byte of the address is odd (LSB is 1), the address is a group address
(broadcast or multicast). The second bit specifies whether the address is globally or
locally administrated (not considered in this chapter).
Ethernet Packet
(Packet)
An Ethernet packet is the collection of bytes that represents the data portion of a
single Ethernet frame on the wire.
Full Duplex
Full-duplex operation allows simultaneous communication between a pair of
stations using point-to-point media (dedicated channel). Full-duplex operation does
not require that transmitters defer, nor do they monitor or react to receive activity,
as there is no contention for a shared medium in this mode. Full-duplex mode can
only be used when all of the following are true:
• The physical medium is capable of supporting simultaneous transmission and
reception without interference.
• There are exactly two stations connected with a full duplex point-to-point link. As
there is no contention for use of a shared medium, the multiple access (that is,
CSMA/CD) algorithms are unnecessary.
• Both stations on the LAN are capable of, and have been configured to use, full-
duplex operation.
The most common configuration envisioned for full-duplex operation consists of a
central bridge (also known as a switch) with a dedicated LAN connecting each
bridge port to a single device.
Full-duplex operation constitutes a proper subset of the MAC functionality required
for half-duplex operation.