Datasheet KSZ8993 (Microchip) - 31

KS8993 Micrel
4B/5B Coding
In 100BaseTX and 100BaseFX the data and frame control are encoded in the transmitter (and decoded in the receiver) using a 4B/5B code. The extra code space is required to encode extra control (frame delineation) points. It is also used to reduce run length as well as supply sufficient transitions for clock recovery. The table below provides the translation for the 4B/5B coding.
Code Type 4B Code 5B Code Value
Data 0000 11110 Data value 0 0001 01001 Data value 1 0010 10100 Data value 2 0011 10101 Data value 3 0100 01010 Data value 4 0101 01011 Data value 5 0110 01110 Data value 6 0111 01111 Data value 7 1000 10010 Data value 8 1001 10011 Data value 9 1010 10110 Data value A 1011 10111 Data value B 1100 11010 Data value C 1101 11011 Data value D 1110 11100 Data value E 1111 11101 Data value F Control Not defined 11111 Idle 0101 11000 Start delimiter part 1 0101 10001 Start delimiter part 2 Not defined 01101 End delimiter part 1 Not defined 00111 End delimiter part 2 Not defined 00100 Transmit error Invalid Not defined 00000 Invalid code Not defined 00001 Invalid code Not defined 00010 Invalid code Not defined 00011 Invalid code Not defined 00101 Invalid code Not defined 00110 Invalid code Not defined 01000 Invalid code Not defined 01100 Invalid code Not defined 10000 Invalid code Not defined 11001 Invalid code
Table 10. 4B/5B Coding
May 2005 31 KS8993