dp83630sqx National Semiconductor Corporation, dp83630sqx Datasheet - Page 30

• Manufacturer Part Number: dp83630sqx
• Description: Precision Phyter - Ieee 1588 Precision Time Protocol Transceiver
• Manufacturer: National Semiconductor Corporation

www.national.com
11.1.1 Code-Group Encoding and Injection
The code-group encoder converts 4-bit (4B) nibble data gen-
erated by the MAC into 5-bit (5B) code-groups for transmis-
sion. This conversion is required to allow control data to be
combined with packet data code-groups. Refer to
4B to 5B code-group mapping details.
The code-group encoder substitutes the first 8-bits of the
MAC preamble with a J/K code-group pair (11000 10001) up-
on transmission. The code-group encoder continues to re-
place subsequent 4B preamble and data nibbles with
corresponding 5B code-groups. At the end of the transmit
packet, upon the deassertion of Transmit Enable signal from
the MAC, the code-group encoder injects the T/R code-group
pair (01101 00111) indicating the end of the frame.
DATA CODES
IDLE AND CONTROL CODES
INVALID CODES
Note: Control code-groups I, J, K, T and R in data fields will be mapped as invalid codes, together with RX_ER asserted.
Name
C
D
H
R
A
B
E
F
K
T
V
V
V
V
V
V
V
V
V
V
0
1
2
3
4
5
6
7
8
9
J
I
TABLE 8. 4B5B Code-Group Encoding/Decoding
PCS 5B Code-Group
11110
01001
10100
10101
01010
01011
01110
01111
10010
10011
10110
10111
11010
11011
11100
11101
00100
11111
11000
10001
01101
00111
00000
00001
00010
00011
00101
00110
01000
01100
10000
11001
Table 8
for
30
HALT code-group - Error code
Inter-Packet IDLE - 0000 (See Note)
First Start of Packet - 0101 (See Note)
Second Start of Packet - 0101 (See Note)
First End of Packet - 0000 (See Note)
Second End of Packet - 0000 (See Note)
After the T/R code-group pair, the code-group encoder con-
tinuously injects IDLEs into the transmit data stream until the
next transmit packet is detected (reassertion of Transmit En-
able).
11.1.2 Scrambler
The scrambler is required to control the radiated emissions at
the media connector and on the twisted pair cable (for
100BASE-TX applications). By scrambling the data, the total
energy launched onto the cable is randomly distributed over
a wide frequency range. Without the scrambler, energy levels
at the PMD and on the cable could peak beyond FCC limita-
tions at frequencies related to repeating 5B sequences (i.e.,
continuous transmission of IDLEs).
MII 4B Nibble Code
0000
0001
0010
0011
0100
0101
0110
0111
1000
1001
1010
1011
1100
1101
1110
1111