TLK105 Datasheet, PDF (25/99 Pages) Texas Instruments – Industrial Temp, Single Port 10/100Mbs Ethernet Physical Layer Transceiver

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TX_CLK
TX_EN
TXD[3:0]
TLK105
TLK106
SLLSEB8A – AUGUST 2012 – REVISED MARCH 2013
Data n-2
[3:0]
Data n-2
[7:4]
Data n-1 Data n-1
[3:0]
[7:4]
Data n
[3:0]
Data n
[7:4]
Error
Code
RX_CLK
RX_DV
RXD[3:0]
Data n-2
[3:0]
Data n-2
[7:4]
Data n-1 Data n-1
[3:0]
[7:4]
Data n
[3:0]
Data n
[7:4]
Error
Code
Don't Care
RX_ER
Figure 5-2. Transmit Code Error Forwarding Diagram
5.1.2 4-Bit to 5-Bit Encoding
The transmit data that is received from the MAC first passes through the 4-Bit to 5-Bit encoder. This block
encodes 4-bit nibble into 5-bit code-groups according to the Table 5-1. 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 they are considered as not valid.
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 4-bit
preamble and data nibbles with corresponding 5-bit code-groups. At the end of the transmit packet, upon
the de-assertion of Transmit Enable signal from the MAC, the code-group encoder adds 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 continuously adds IDLEs into the transmit data
stream until the next transmit packet is detected.
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