High-Performance Single-Chip 10/100 Ethernet Controller with HP Auto-MDIX
Datasheet
Chapter 4 Internal Ethernet PHY
4.1
Top Level Functional Description
Functionally, the internal PHY can be divided into the following sections:
100Base-TX transmit and receive
10Base-T transmit and receive
Internal MII interface to the Ethernet Media Access Controller
Auto-negotiation to automatically determine the best speed and duplex possible
Management Control to read status registers and write control registers
100M
TX_CLK
PLL
MAC
4B/5B
Encoder
Scrambler
and PISO
Internal
MII 25 MHz by 4 bits
25MHz
by 4 bits
25MHz by
5 bits
MII
125 Mbps Serial
NRZI
Converter
MLT-3
Converter
Tx
Driver
NRZI
MLT-3
MLT-3
Magnetics
MLT-3
MLT-3
RJ45
CAT-5
Figure 4.1 100Base-TX Data Path
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
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 5th transmit data bit is equivalent to TX_ER.
Revision 1.5 (07-18-06)
SMSC LAN9218
DATA5S6HEET
SMSC [ SMSC CORPORATION ]
