8101 datasheet(46/172 Pages) LSI

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2-28

Functional Description

2.11.2 8B10B Decoder

The 8B10B decoder performs the reverse process of the 8B10B encoder.

The 8B10B decoder converts each 10-bit word back into an 8-bit byte

using the code conversion tables deﬁned in IEEE 802.3z and shown in

Table 2.7 (in abbreviated form) and Table 2.8. The 8B10B decoder also

checks the running disparity of the incoming 10B word to insure that it is

correct.

A PCS codeword error results if the 8B10B decoder detects any of the

following:

• A 10B word that is not valid (does not appear in Table 2.7)

• An ordered set that is not valid (does not appear in Table 2.8)

• An error in the running disparity

Packets with PCS codeword errors are normally discarded. Refer to

Section 2.13, “Packet Discard” for more details on discards. Clearing the

DIS_CWRD bit in “Register 8–Conﬁguration 2‚" Section 4.3.9, programs

the controller to not discard a packet with PCS codeword errors.

Table 2.8

10B Deﬁned Ordered Sets

10B Code

Symbol

Description

10B Codes

Begin

End

/C1/

Link

Conﬁguration 1

/K28.5/1

/D21.5/

conﬁg_word1

conﬁg_word2

+ or -

ﬂip2

/C2/

Link

Conﬁguration 2

/K28.5/1

/D2.2/

conﬁg_word1

conﬁg_word2

+or

−

same2

/C/

Link

Conﬁguration

Alternating

/C1/ & /C2/

––

/I1/

Idle 1

/K28.5/

/D5.6/

+–

/I2/

Idle 2

/K28.5/

/D16.2/

––

/I/

Idle

/I1/ or /I2/

–

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