Small Footprint RMII 10/100 Ethernet Transceiver with HP Auto-MDIX Support
Datasheet
Chapter 3 Functional Description
This chapter provides functional descriptions of the various device features. These features have been
categorized into the following sections:
Transceiver
Auto-negotiation
HP Auto-MDIX Support
MAC Interface
Serial Management Interface (SMI)
Interrupt Management
Configuration Straps
Miscellaneous Functions
Application Diagrams
3.1
Transceiver
3.1.1
100BASE-TX Transmit
The 100BASE-TX transmit data path is shown in Figure 3.1. Each major block is explained in the
following subsections.
PLL
MAC
Ext Ref_CLK
4B/5B
Encoder
Scrambler
and PISO
25MHz
by 4 bits
25MHz by
5 bits
RMII 50Mhz by 2 bits
RMII
NRZI
Converter
MLT-3
Converter
Tx
Driver
125 Mbps Serial
NRZI
MLT-3
MLT-3
MLT-3
MLT-3
Magnetics
RJ45
CAT-5
Figure 3.1 100BASE-TX Transmit Data Path
3.1.1.1
100BASE-TX Transmit Data Across the RMII Interface
The MAC controller drives the transmit data onto the TXD bus and asserts TXEN to indicate valid data.
The data is latched by the transceiver’s RMII block on the rising edge of REF_CLK. The data is in the
form of 2-bit wide 50MHz data.
SMSC LAN8720A/LAN8720Ai
17
Revision 1.4 (08-23-12)
DATASHEET
SMSC [ SMSC CORPORATION ]
