Architecture
714
SPRUH82C – April 2013 – Revised September 2016
Copyright © 2013–2016, Texas Instruments Incorporated
EMAC/MDIO Module
Term
Meaning
Half Duplex
In half-duplex mode, the CSMA/CD media access method is the means by which
two or more stations share a common transmission medium. To transmit, a station
waits (defers) for a quiet period on the medium, that is, no other station is
transmitting. It then sends the intended message in bit-serial form. If, after initiating
a transmission, the message collides with that of another station, then each
transmitting station intentionally transmits for an additional predefined period to
ensure propagation of the collision throughout the system. The station remains
silent for a random amount of time (backoff) before attempting to transmit again.
Host
The host is an intelligent system resource that configures and manages each
communications control module. The host is responsible for allocating memory,
initializing all data structures, and responding to port (EMAC) interrupts. In this
chapter, host refers to the device.
Jabber
A condition wherein a station transmits for a period of time longer than the
maximum permissible packet length, usually due to a fault condition.
Link
The transmission path between any two instances of generic cabling.
Multicast MAC
Address
A class of MAC address that sends a packet to potentially more than one recipient.
A group address is specified by setting the LSB of the first MAC address byte to 1.
Thus, 01h-02h-03h-04h-05h-06h is a valid multicast address. Typically, an Ethernet
MAC looks for only certain multicast addresses on a network to reduce traffic load.
The multicast address list of acceptable packets is specified by the application.
Physical Layer and
Media Notation
To identify different Ethernet technologies, a simple, three-field, type notation is
used. The Physical Layer type used by the Ethernet is specified by these fields:
<data rate in Mb/s><medium type><maximum segment length (×100m)>
The definitions for the technologies mentioned in this chapter are:
• 10Base-T: IEEE 802.3 Physical Layer specification for a 10 Mb/s CSMA/CD local
area network over two pairs of twisted-pair telephone wire.
• 100Base-T: IEEE 802.3 Physical Layer specification for a 100 Mb/s CSMA/CD
local area network over two pairs of Category 5 unshielded twisted-pair (UTP) or
shielded twisted-pair (STP) wire.
• Twisted pair: A cable element that consists of two insulated conductors twisted
together in a regular fashion to form a balanced transmission line.
Port
Ethernet device.
Promiscuous Mode EMAC receives frames that do not match its address.
18.2 Architecture
This section discusses the architecture and basic function of the EMAC/MDIO module.
18.2.1 Clock Control
All internal EMAC logic is clocked synchronously on one clock domain. See your device-specific data
manual for information.
The MDIO clock is based on a divide-down of the peripheral clock and is specified to run up to 2.5 MHz
(although typical operation would be 1.0 MHz). Because the peripheral clock frequency is variable, the
application software or driver must control the divide-down value.
The transmit and receive clock sources are provided by the external PHY to the MII_TXCLK and
MII_RXCLK pins or to the RMII reference clock pin. Data is transmitted and received with respect to the
reference clocks of the interface pins.