LAN8740A Datasheet, PDF (17/136 Pages) Microchip Technology – Small Footprint MII/RMII 10/100 Energy Efficient Ethernet Transceiver with HP Auto-MDIX and flexPWR® Technology

LAN8740A/LAN8740Ai
3.0 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.
FIGURE 3-1:
100BASE-TX TRANSMIT DATA PATH
MAC
TX_CLK
(for MII only)
PLL
Ext Ref_CLK (for RMII only)
MII 25 MHz by 4 bits
or
RMII 50 MHz by 2 bits
MII/RMII
25 MHz
by 4 bits
4B/5B 25 MHz by Scrambler
Encoder ^{5 bits} and PISO
125 Mbps Serial
NRZI
Converter
NRZI
MLT-3
Converter
MLT-3
Tx
Driver
MLT-3 Magnetics MLT-3
RJ45
MLT-3
CAT-5
3.1.1.1 100BASE-TX Transmit Data Across the MII/RMII Interface
For MII, 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 MII block on the rising edge of TXCLK. The data is in the form of 4-bit wide 25 MHz data.
For RMII, 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 50
MHz data.
3.1.1.2 4B/5B Encoding
The transmit data passes from the MII/RMII block to the 4B/5B encoder. This block encodes the data from 4-bit nibbles
to 5-bit symbols (known as “code-groups”) according to Table 3-1. Each 4-bit data-nibble is mapped to 16 of the 32 pos-
sible code-groups. The remaining 16 code-groups are either used for control information or are not valid.
The first 16 code-groups are referred to by the hexadecimal values of their corresponding data nibbles, 0 through F. The
remaining code-groups are given letter designations with slashes on either side. For example, an IDLE code-group is
/I/, a transmit error code-group is /H/, etc.
 2013-2015 Microchip Technology Inc.
DS00001987A-page 17