DP83848VYB National Semiconductor, DP83848VYB Datasheet - Page 21

• Manufacturer Part Number: DP83848VYB
• Description: TRANSCEIVER, ENET PHY, 10/100, 48LQFP
• Manufacturer: National Semiconductor

Specifications of DP83848VYB

• Data Rate: 100Mbps
• No. Of Ports: 1
• Ethernet Type: IEEE 802.3u
• Supply Current: 92mA
• Supply Voltage Range: 3V To 3.6V
• Operating Temperature Range: -40°C To +105°C
• Digital Ic Case Style: LQFP
• No.: RoHS Compliant
• Interface Type: MII Serial, RMII
• Rohs Compliant: Yes
• Lead Free Status / Rohs Status: Not Compliant

4.1.1 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 Table 6 for
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.
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).
DATA CODES
IDLE AND CONTROL CODES
INVALID CODES
Note 1: Control code-groups I, J, K, T and R in data fields will be mapped as invalid codes, together with RX_ER asserted.
C
D
H
R
0
1
2
3
4
5
6
7
8
9
A
B
E
F
K
T
V
V
V
V
V
V
V
V
J
I
TABLE 6. 4B5B Code-Group Encoding/Decoding
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
21
HALT code-group - Error code
Inter-Packet IDLE - 0000 (Note 1)
First Start of Packet - 0101 (Note 1)
Second Start of Packet - 0101 (Note 1)
First End of Packet - 0000 (Note 1)
Second End of Packet - 0000 (Note 1)
4.1.2 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).
The scrambler is configured as a closed loop linear feedback
shift register (LFSR) with an 11-bit polynomial. The output of
the closed loop LFSR is X-ORd with the serial NRZ data from
the code-group encoder. The result is a scrambled data
stream with sufficient randomization to decrease radiated
emissions at certain frequencies by as much as 20 dB. The
DP83848VYB uses the PHY_ID (pins PHYAD [4:1]) to set a
unique seed value.
0000
0001
0010
0011
0100
0101
0110
0111
1000
1001
1010
1011
1100
1101
1110
1111
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