LAN8700 Datasheet, PDF (14/74 Pages) SMSC Corporation – ±15kV ESD Protected MII/RMII Fast-Ethernet PHY with HP Auto-MDIX and SMSC flexPWR TM in a Small Footprint

LAN8700/LAN8700i
4.0 ARCHITECTURE DETAILS
4.1 Top Level Functional Architecture
Functionally, the PHY can be divided into the following sections:
• 100Base-TX transmit and receive
• 10Base-T transmit and receive
• MII or RMII interface to the controller
• Auto-negotiation to automatically determine the best speed and duplex possible
• Management Control to read status registers and write control registers
FIGURE 4-1:
100BASE-TX DATA PATH
MAC
TX_CLK
(for M II only)
Ext R ef_C LK (for R M II only)
M II 25 M hz by 4 bits
or
M II
R M II 50M hz by 2 bits
100M
PLL
25MHz
by 4 bits
4 B /5 B
Encoder
25M Hz by S cram bler
5 bits
and PISO
NRZI
C o n ve rte r
NRZI
125 M bps Serial
M LT-3
C o n ve rte r
M LT -3
Tx
D riv e r
MLT-3 M agnetics
RJ45
M LT -3
M LT -3
C A T -5
4.2 100Base-TX Transmit
The data path of the 100Base-TX is shown in Figure 4-1. Each major block is explained below.
4.2.1 100M TRANSMIT DATA ACROSS THE MII/RMII INTERFACE
For MII, the MAC controller drives the transmit data onto the TXD bus and asserts TX_EN to indicate valid data. The
data is latched by the PHY’s MII block on the rising edge of TX_CLK. The data is in the form of 4-bit wide 25MHz data.
The MAC controller drives the transmit data onto the TXD bus and asserts TX_EN to indicate valid data. The data is
latched by the PHY’s MII block on the rising edge of REF_CLK. The data is in the form of 2-bit wide 50MHz data.
4.2.2 4B/5B ENCODING
The transmit data passes from the MII 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 4-1. Each 4-bit data-nibble is mapped to 16 of the 32 possible
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.
The encoding process may be bypassed by clearing bit 6 of register 31. When the encoding is bypassed the 5^th transmit
data bit is equivalent to TX_ER.
Note that encoding can be bypassed only when the MAC interface is configured to operate in MII mode.
DS00002260A-page 14
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