TLK1221 Datasheet, PDF (12/23 Pages) Texas Instruments – ETHERNET TRANSCEIVER

TLK1221
SLLS713 – FEBRUARY 2007
APPLICATION INFORMATION
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8b/10b Transmission Code
The PCS maps GMII signals into ten-bit code groups and vice versa, using an 8b/10b block coding scheme. The
PCS uses the transmission code to improve the transmission characteristics of information to be transferred
across the link. The encoding defined by the transmission code ensures that sufficient transitions are present in
the PHY bit stream to make clock recovery possible in the receiver. Such encoding also greatly increases the
likelihood of detecting any single- or multiple-bit errors that may occur during transmission and reception of
information. The 8b/10b transmission code specified for use has a high transition density, is run length limited,
and is dc-balanced. The transition density of the 8b/10b symbols ranges from 3 to 8 transitions per symbol. The
definition of the 8b/10b transmission code is specified in IEEE 802.3 Gigabit Ethernet and ANSI X3.230-1994
(FC-PH), clause 11.
8b/10b transmission code uses letter notation describing the bits of an unencoded information octet. The bit
notation of A, B, C, D, E, F, G, H for an unencoded information octet is used in the description of the 8b/10b
transmission code-groups, where A is the LSB. Each valid code group has been given a name using the
following convention: /Dx.y/ for the 256 valid data code-groups and /Kx.y/ for the special control code-groups,
where y is the decimal value of bits EDCBA and x is the decimal value of bits HGF (noted as K<HGF.EDCBA>).
Thus, an octet value of FE representing a code-group value of K30.7 would be represented in bit notation as
111 11110.
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