AM79C875KI AMD (ADVANCED MICRO DEVICES), AM79C875KI Datasheet - Page 13

• Manufacturer Part Number: AM79C875KI
• Manufacturer: AMD (ADVANCED MICRO DEVICES)

Specifications of AM79C875KI

• Lead Free Status / RoHS Status: Not Compliant

FUNCTIONAL DESCRIPTION
Overview
The NetPHY™ 4LP transceiver is a four-port CMOS
device that implements the complete physical layer for
10BASE-T and the Physical Coding Sublayer (PCS),
Physical Medium Attachment (PMA), and Physical Me-
dium Dependent (PMD) functionality for 100BASE-TX.
The NetPHY™ 4LP transceiver implements Auto-Ne-
gotiation allowing two devices connected across a link
segment to take maximum advantage of their capabili-
ties. Auto-Negotiation is performed as defined in the
IEEE 802.3u specification.
The NetPHY™ 4LP device communicates with a
switch or MAC device through the Reduced Media In-
dependent Interface (RMII).
The NetPHY™ 4LP device consists of the following
functional blocks:
■ RMII Functional Blocks
■ 100BASE-X Block including:
■ 10BASE-T Block including:
■ Carrier Integrity Monitor
■ Auto-Negotiation
■ Status LEDs
■ PHY Control and Management
Modes of Operation
The RMII interface provides the data path connection
between the NetPHY™ 4LP transceivers and the
Media Access Controller (MAC), repeater, or switch de-
vices. The MDC and MDIO pins are responsible for
communication between the NetPHY™ 4LP trans-
ceiver and the station management entity (STA).
— Transmit and Receive State Machines
— 4B/5B Encoder and Decoder
— Stream Cipher Scrambler and Descrambler
— Link Monitor State Machine
— Far End Fault Indication (FEFI) State Machine
— MLT-3 Encoder
— MLT-3 Decoder with adaptive equalization
— Manchester Encoder/Decoder
— Jabber
— Receive Polarity Detect
— Waveshaping and Filtering
Am79C875
The RMII standard reduces the pin count by halving the
number of data pins, eliminating pins not used in switch
applications, and using a single global clock. Each port
has an independent RMII.
RMII uses seven pins per port. They are as follows:
Receive Data
Carrier Sense
Receive Error
Transmit Data
Transmit Enable
Note: [X] refers to the port.
In RMII mode, REF_CLK must be sourced by a
50-MHz clock signal.
RMII Pin Descriptions
CRS_DV
Carrier Sense/Receive Data Valid
CRS_DV is asserted by the PHY when the receive me-
dium is non-idle. Loss of carrier results in the deasser-
tion of CRS_DV synchronous to the cycle of REF_CLK,
which presents the first di-bit of a nibble onto RXD[1:0]
(i.e., CRS_DV is deasserted only on nibble bound-
aries). If the PHY has additional bits to be presented on
RXD[1:0] following the initial deassertion of CRS_DV,
the PHY asserts CRS_DV on cycles of REF_CLK
which present the second di-bit of each nibble. The
PHY deasserts CRS_DV on cycles of REF_CLK which
present the first di-bit of the nibble. As a result, starting
on the byte boundaries, CRS_DV toggles at 25 MHz in
100 Mbps mode and 2.5 MHz in 10 Mbps mode when
CRS ends before RX_DV (i.e., the FIFO still has bits to
transfer when the carrier event ends). Therefore, the
MAC can accurately recover RX_DV and CRS. Refer
to Figure 1.
During a false carrier event, CRS_DV remains as-
serted for the duration of carrier activity. Refer to
Figure 2.
The data on RXD[1:0] is considered valid once
CRS_DV is asserted. However, since the assertion of
CRS_DV is asynchronous relative to REF_CLK, the
data on RXD[1:0] is “00” until proper receive signal
decoding takes place.
Note: CRS_DV is asserted asynchronously in order
to minimize latency of control signals through the PHY.
RXD[X]_[1:0]
CRS_DV[X]
RX_ER[X]
TXD[X]_[1:0]
TX_EN[X]
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