lan9221 Standard Microsystems Corp., lan9221 Datasheet - Page 68

• Manufacturer Part Number: lan9221
• Description: High-performance 16-bit Non-pci 10/100 Ethernet Controller With Variable Voltage I/o
• Manufacturer: Standard Microsystems Corp.

Chapter 4 Internal Ethernet PHY
Revision 2.6 (12-04-08)
4.1
4.2
4.2.1
Functionally, the internal PHY can be divided into the following sections:
The data path of the 100Base-TX is shown in
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
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
Top Level Functional Description
100Base-TX Transmit
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
MAC
Converter
NRZI
RJ45
th
MII 25 MHz by 4 bits
transmit data bit is equivalent to TX_ER.
TX_CLK
NRZI
Internal
MLT-3
Figure 4.1 100Base-TX Data Path
Converter
MLT-3
100M
PLL
CAT-5
DATASHEET
125 Mbps Serial
MII
MLT-3
MLT-3
68
High-Performance 16-bit Non-PCI 10/100 Ethernet Controller with Variable Voltage I/O
Figure
by 4 bits
Driver
25MHz
Tx
4.1. Each major block is explained below.
Encoder
4B/5B
MLT-3
Magnetics
25MHz by
5 bits
Table
4.1. Each 4-bit data-nibble
Scrambler
and PISO
SMSC LAN9221/LAN9221i
Datasheet