DP83815CVNG National Semiconductor, DP83815CVNG Datasheet - Page 21

• Manufacturer Part Number: DP83815CVNG
• Description: IC CONTROLLER MEDIA ACCESS
• Manufacturer: National Semiconductor

Specifications of DP83815CVNG

• Controller Type: Ethernet Controller, MAC/BIU
• Interface: PCI
• Voltage - Supply: 3.3V
• Current - Supply: 170mA
• Operating Temperature: 0°C ~ 70°C
• Mounting Type: Surface Mount
• Package / Case: 144-LQFP
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Other names: *DP83815CVNG

Subject to change without notice.
3.0 Functional Description
3.9.1 Code-group Encoding and Injection
The code-group encoder converts 4-bit (4B) nibble data
generated by the MAC into 5-bit (5B) code-groups for
transmission. This conversion is required to allow control
data to be combined with packet data code-groups. Refer
to Table 3-1 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)
upon transmission. The code-group encoder continues to
replace subsequent 4B preamble and data nibbles with
corresponding 5B code-groups. At the end of the transmit
packet, upon the de-assertion of Transmit Enable signal
from the MAC, the code-group encoder injects the T/R
code-group pair (01101 00111) indicating the end of frame.
After the T/R code-group pair, the code-group encoder
continuously injects IDLEs into the transmit data stream
until the next transmit packet is detected (re-assertion of
Transmit Enable).
FROM CGM
BP_4B5B
Figure 3-6 100BASE-TX Transmit Block Diagram
BP_SCR
(Continued)
100BASE-TX
LOOPBACK
TXCLK
GROUP ENABLER
TXD(3:0)/TXER
4B5B CODE-
5B PARALLEL
SCRAMBLER
TO SERIAL
21
MUX
TD +/-
3.9.2 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 limitations 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.
NRZ TO NRZI
TO MLT-3/
COMMON
MUX
BINARY
DRIVER
ENCODER
MUX
Rev O
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