AM79C873 Advanced Micro Devices, AM79C873 Datasheet - Page 12

• Manufacturer Part Number: AM79C873
• Description: NetPHY -1 10/100 Mbps Ethernet Physical Layer Single-Chip Transceiver with 100BASE-FX Support
• Manufacturer: Advanced Micro Devices

FUNCTIONAL DESCRIPTION
The NetPHY-1 Fast Ethernet single-chip transceiver,
provides the functionality as specified in the IEEE
802.3u standard, integrates complete 100BASE-FX,
100BASE-TX modules and a complete 10BASE-T
module. The NetPHY-1 device provides a Media Inde-
pendent Interface (MII) as defined in the IEEE 802.3u
standard (Clause 22).
MII Interface
The purpose of the MII interface is to provide a simple,
easy to implement connection between the MAC Rec-
onciliation layer and the PHY. The MII is designed to
make the differences between various media transpar-
ent to the MAC sublayer.
The MII consists of a nibble wide receive data bus, a
nibble wide transmit data bus, and control signals to fa-
cilitate data transfers between the PHY and the Recon-
ciliation layer.
12
TXD (transmit data) is a nibble (4 bits) of data that
are driven by the reconciliation sublayer synchro-
nously with respect to TX_CLK. For each TX_CLK
period which TX_EN is asserted, TXD (3:0) are ac-
cepted for transmission by the PHY.
TX_CLK (transmit clock) output to the MAC recon-
ciliation sublayer is a continuous clock that provides
the timing reference for the transfer of the TX_EN,
TXD, and TX_ER signals.
MII Interface
Figure 1. Functional Block Diagram
P R E L I M I N A R Y
Carrier
Sense
Management
MII Serial
Interface
Am79C873
Detection
Transmitter
Collision
Tranceiver
10Base-T
100Base
100Base
Receiver
The NetPHY-1 device performs all Physical Coding
Sublayer (PCS), Physical Media Access (PMA),
Twisted Pair Physical Medium Dependent (TP-PMD)
sublayer, 10BASE-T Encoder/Decoder, and Twisted
Pair Media Access Unit (TPMAU) functions. Figure 1
shows the major functional blocks implemented in the
NetPHY-1 device.
TX_EN (transmit enable) input from the MAC recon-
ciliation sublayer to indicate nibbles are being
sented on the MII for transmission on the physical
medium. TX_ER (transmit coding error) transitions
synchronously with respect to TX_CLK. If TX_ER is
asserted for one or more clock periods, and TX_EN
is asserted, the PHY will emit one or more symbols
that are not part of the valid data delimiter set some-
where in the frame being transmitted.
RXD (receive data) is a nibble (4 bits) of data that
are sampled by the reconciliation sublayer syn-
chronously with respect to RX_CLK. For each
RX_CLK period which RX_DV is asserted, RXD
(3:0) are transferred from the PHY to the MAC
reconciliation sublayer.
RX_CLK (receive clock) output to the MAC reconcil-
iation sublayer is a continuous clock that provides
the timing reference for the transfer of the RX_DV,
RXD, and RX_ER signals.
Negotiation
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