AM79C975 datasheet(82/304 Pages) AMD

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Am79C973/Am79C975

P R E L I M INARY

Encoder

The encoder converts the 4-bit nibble from the MII into

five-bit code-groups, using a 4B/5B block coding

scheme. The encoder operates on the 4-bit data nibble

independent of the code-group b oundar y. The

100BASE-X physical protocol data unit is called a

stream. The encoding method used provides the fol-

lowing:

s Adequate codes (32) to provide for all data code-

groups (16) plus necessary control code-groups.

s Appropriate coding efficiency (4 data bits per 5

code-bits; 80%) to implement a 100-Mbps physical

layer interface on a 125-Mbps physical channel.

s Sufficient transition density to facilitate clock recov-

ery (when not scrambled).

The code-group mapping is defined in Table 8.

Table 8. Encoder Code-Group Mapping

TXD[3:0]

Name

PCS Code-Group

Interpretation

0 0 0 0

1 1 1 1 0

Data 0

0 0 0 1

0 1 0 0 1

Data 1

0 0 1 0

1 0 1 0 0

Data 2

0 0 1 1

1 0 1 0 1

Data 3

0 1 0 0

0 1 0 1 0

Data 4

0 1 0 1

0 1 0 1 1

Data 5

0 1 10

0 1 1 1 0

Data 6

0 1 1 1

0 1 1 1 1

Data 7

1 0 0 0

1 0 0 1 0

Data 8

1 0 0 1

1 0 0 1 1

Data 9

1 0 1 0

1 0 1 1 0

Data A

1 0 1 1

1 0 1 1 1

Data B

1 1 0 0

1 1 0 1 0

Data C

1 1 0 1

1 1 0 1 1

Data D

1 1 1 0

1 1 1 0 0

Data E

1 1 1 1

1 1 1 0 1

Data F

Undefined

1 1 1 1 1

IDLE; used as inter-Stream fill code

0 1 0 1

1 1 0 0 0

Start-of-Stream Delimiter, Part 1 of 2; always used

in pairs with K

0 1 0 1

1 0 0 0 1

Start-of-Stream Delimiter, Part 2 of 2; always used

in pairs with J

Undefined

0 1 1 0 1

End-of-Stream Delimiter, Part 1 of 2; always used in

pairs with R

Undefined

0 0 1 1 1

End-of-Stream Delimiter, Part 2 of 2; always used in

pairs with T

Undefined

0 0 1 0 0

Transmit Error; used to force signaling errors

Undefined

0 0 0 0 0

Invalid Code

Undefined

0 0 0 0 1

Invalid Code

Undefined

0 0 0 1 0

Invalid Code

Undefined

0 0 0 1 1

Invalid Code

Undefined

0 0 1 0 1

Invalid Code

Undefined

0 0 1 1 0

Invalid Code

Undefined

0 1 0 0 0

Invalid Code

Undefined

0 1 1 0 0

Invalid Code

Undefined

1 0 0 0 0

Invalid Code

Undefined

1 1 0 0 1

Invalid Code

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