LAN83C183 datasheet(21/113 Pages) SMSC

21 / 113 page

SMSC DS – LAN83C183

Rev. 12/14/2000

The 4B5B encoder takes 4B (four-bit) nibbles from the Transmit MAC block, converts

them into 5B (five-bit) words according to Table 1.4, and sends the 5B words to the

scrambler. The 4B5B encoder also substitutes the first eight bits of the preamble with

the Start of Stream Delimiter (SSD) (/J/K/ symbols) and adds an End of Stream

Delimiter (ESD) (/T/R/ symbols) to the end of each packet, as defined in IEEE 802.3

and shown in Figure 1.2. The 4B5B encoder also fills the period between packets

(idle period), with a continuous stream of idle symbols, as shown in Figure 1.2.

1.2.3.2 MANCHESTER ENCODER (10 MBITS/S)

The Manchester Encoder shown in Figure 1.1 is used for 10 Mbits/s operation. It

combines clock and non-return to zero inverted (NRZI) data such that the first half of

Table 1.4 4B/5B Symbol Mapping

Symbol Name

Description

5B Code

4B Code

Data 0

11110

0000

Data 1

01001

0001

Data 2

10100

0010

Data 3

10101

0011

Data 4

01010

0100

Data 5

01011

0101

Data 6

01110

0110

Data 7

01111

0111

Data 8

10010

1000

Data 9

10011

1001

Data A

10110

1010

Data B

10111

1011

Data C

11010

1100

Data D

11011

1101

Data E

11100

1110

Data F

11101

1111

Idle

11111

0000

SSD #1

11000

0101

SSD #2

10001

0101

ESD #1

01101

0000

ESD #2

00111

0000

Halt

00100

Undefined

---

Invalid codes

All others1

0000

1. These 5B codes are not used. The decoder converts them

to a 4B code of 0000. The encoder converts the 4B 0000

code to the 5B 11110 code, as shown in symbol 0.

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