编辑“︁8b/10b”︁（章节）

== 工作原理 ==
8b/10b編碼輸出位元數目總共是10個位元，但只有「+2」「+0」「-2」三種組合。其中「+2」是指4個位元0，與6個位元1；「+0」是指5個位元“0”，與5個位元“1”；「-2」是指6個位元“0”，與4個位元“1”，利用這種「不均等性— Disparity」的特性而具有強大的直流平衡（DC Balance）功能，可使得发送的“0”、“1”数量保持一致，连续的“1”或“0”基本上不超过5位。

(Disparity = number of "1" - number of "0")

=== 編碼表 ===
8b/10b编码将一组8位元資料分成两组，一组3位元，一组5位元，經過編碼後形成一组4位元和一组6位元，故送發時是一組10位元的資料，解码時再将10位元的資料变换得到8位元資料。編碼過程中低位5位元的資料会进行5B/6B编码，高位3位元的資料则进行3B/4B编码。

例如一組8位元的資料是 10110101：

首先，分成兩組 101 與 10101

a=10101（21） b=101（5），符號為 D21.5，在下表中的位序为'''HGFEDCBA'''，a（EDCBA）经过5B/6B编码为abcdei，b（HGF）经过3B/4B编码为fghj。

RD = Running Disparity.

{| class="wikitable" style="text-align:center"
|+不均等性的執行規則
|-
! Previous RD !! Disparity of 6 or 4 Bit Code !! Disparity chosen !! Next RD
|-
| −1 ||  0 ||  0 || −1
|-
| −1 || ±2 || +2 || +1
|-
| +1 ||  0 ||  0 || +1
|-
| +1 || ±2 || −2 || −1
|}

==== 5b/6b ====
{| class=wikitable style=text-align:center
|+ 5B/6B code
|-
!colspan=2| input !! RD = −1 !! RD = +1 
|rowspan=19|
!colspan=2| input !! RD = −1 !! RD = +1 
|-
!      !! EDCBA !!colspan=2| abcdei !!      !! EDCBA !!colspan=2| abcdei
|-
| D.00 || 00000 || 100111 || 011000 || D.16 || 10000 || 011011 || 100100
|-
| D.01 || 00001 || 011101 || 100010 || D.17 || 10001 ||colspan=2| 100011
|-
| D.02 || 00010 || 101101 || 010010 || D.18 || 10010 ||colspan=2| 010011
|-
| D.03 || 00011 ||colspan=2| 110001 || D.19 || 10011 ||colspan=2| 110010
|-
| D.04 || 00100 || 110101 || 001010 || D.20 || 10100 ||colspan=2| 001011
|-
| D.05 || 00101 ||colspan=2| 101001 || D.21 || 10101 ||colspan=2| 101010
|-
| D.06 || 00110 ||colspan=2| 011001 || D.22 || 10110 ||colspan=2| 011010
|-
| D.07 || 00111 || 111000 || 000111 || D.23 † || 10111 || 111010 || 000101
|-
| D.08 || 01000 || 111001 || 000110 || D.24 || 11000 || 110011 || 001100
|-
| D.09 || 01001 ||colspan=2| 100101 || D.25 || 11001 ||colspan=2| 100110
|-
| D.10 || 01010 ||colspan=2| 010101 || D.26 || 11010 ||colspan=2| 010110
|-
| D.11 || 01011 ||colspan=2| 110100 || D.27 † || 11011 || 110110 || 001001
|-
| D.12 || 01100 ||colspan=2| 001101 || D.28 || 11100 ||colspan=2| 001110
|-
| D.13 || 01101 ||colspan=2| 101100 || D.29 † || 11101 || 101110 || 010001
|-
| D.14 || 01110 ||colspan=2| 011100 || D.30 † || 11110 || 011110 || 100001
|-
| D.15 || 01111 || 010111 || 101000 || D.31 || 11111 || 101011 || 010100
|-
|colspan=4|                         || K.28 || 11100 || 001111 || 110000
|}

† Same code is used for K.x.7

==== 3b/4b ====
{| class="wikitable" style="text-align:center"
|+ 3b/4b code
|-
!colspan=2| input !! RD = −1 !! RD = +1
|rowspan=11|
!colspan=2| input !! RD = −1 !! RD = +1 
|-
!      !! HGF !!colspan=2| fghj !!      !! HGF !!colspan=2| fghj
|-
| D.x.0 || 000 || 1011   || 0100|| K.x.0 || 000 || 1011   || 0100
|-
| D.x.1 || 001 ||colspan=2| 1001|| K.x.1 ‡ || 001 || 0110   || 1001
|-
| D.x.2 || 010 ||colspan=2| 0101|| K.x.2 ‡ || 010 || 1010   || 0101
|-
| D.x.3 || 011 || 1100   || 0011|| K.x.3 || 011 || 1100   || 0011
|-
| D.x.4 || 100 || 1101   || 0010|| K.x.4 || 100 || 1101   || 0010
|-
| D.x.5 || 101 ||colspan=2| 1010|| K.x.5 ‡ || 101 || 0101   || 1010
|-
| D.x.6 || 110 ||colspan=2| 0110|| K.x.6 ‡ || 110 || 1001   || 0110
|-
| D.x.P7 † || 111 || 1110  || 0001|| || || |
|-
| D.x.A7 † || 111 || 0111  || 1000|| K.x.7 † ‡ || 111 || 0111  || 1000
|}
<!--
† For D.x.7, the Primary (D.x.P7) or Alternate (D.x.A7) encoding must be selected in order to avoid a run of five consecutive 0s or 1s when combined with the preceding 5b/6b code.  Sequences of five identical bits are used in comma codes for synchronization issues.  D.x.A7 is only used for x=17, x=18, and x=20 when RD=−1 and for  x=11, x=13, and x=14 when RD=+1. With x=23, x=27, x=29, and x=30, the same code forms the control codes K.x.7. Any other x.A7 code can't be used as it would result in chances for misaligned comma sequences.

‡ The alternate encoding for the K.x.y codes with disparity 0 allow for K.28.1, K.28.5, and K.28.7 to be "comma" codes that contain a bit sequence that can't be found elsewhere in the data stream.
-->
==== Control symbols ====
<!--
The control symbols within 8b/10b are 10b bytes that are valid sequences of bits (no more than six 1s or 0s) but do not have a corresponding 8b data byte.  They are used for low-level control functions.  For instance, in Fibre Channel, K28.5 is used at the beginning of four-byte sequences (called "Ordered Sets") that perform functions such as Loop Arbitration, Fill Words, Link Resets, etc.
-->
5b/6b 與 3b/4b 表可能導致下列 12 控制符號（control symbols）允許被發送，K.28.1， K.28.5， K.28.7 是逗号（，）序列：
{| class="wikitable" style="text-align:center"
|+ 控制符號（Control symbols）
|-
! colspan=2 | input !! RD = −1 !! RD = +1
|-
!              !! HGF EDCBA !! abcdei fghj !! abcdei fghj
|-
| K.28.0       || 000 11100 || 001111 0100 || 110000 1011
|-
| K.28.1 †     || 001 11100 || 001111 1001 || 110000 0110
|-
| K.28.2&nbsp; || 010 11100 || 001111 0101 || 110000 1010
|-
| K.28.3&nbsp; || 011 11100 || 001111 0011 || 110000 1100
|-
| K.28.4&nbsp; || 100 11100 || 001111 0010 || 110000 1101
|-
| K.28.5 †     || 101 11100 || 001111 1010 || 110000 0101
|-
| K.28.6&nbsp; || 110 11100 || 001111 0110 || 110000 1001
|-
| K.28.7 ‡     || 111 11100 || 001111 1000 || 110000 0111
|-
| K.23.7&nbsp; || 111 10111 || 111010 1000 || 000101 0111
|-
| K.27.7&nbsp; || 111 11011 || 110110 1000 || 001001 0111
|-
| K.29.7&nbsp; || 111 11101 || 101110 1000 || 010001 0111
|-
| K.30.7&nbsp; || 111 11110 || 011110 1000 || 100001 0111
|}
<!--
† Within the control symbols, K.28.1, K.28.5, and K.28.7 are "comma symbols".  Comma symbols are used for synchronization (finding the alignment of the 8b/10b codes within a bit-stream).  If K.28.7 is not used, the unique comma sequences 0011111 or 1100000 cannot be found at any bit position within any combination of normal codes.

‡ If K.28.7 is allowed in the actual coding, a more complex definition of the synchronization pattern than suggested by † needs to be used, as a combination of K.28.7 with several other codes forms a false misaligned comma symbol overlapping the two codes. A sequence of multiple K.28.7 codes is not allowable in any case, as this would result in undetectable misaligned comma symbols.

K.28.7 is the only comma symbol that cannot be the result of a single bit error in the data stream.
-->