12B/14B Line Code

Purpose

The 12B/14B line code is designed to provide a DC balanced encoding scheme for transmitting 12-bit data words over high speed serial links.

Code Table

Encoding Algorithm

Like 8B/10B, the code table is split into two parts. The 7 least significant bits are encoded using a 7B/8B encoding table, and the 5 most significant bits are encoding using a 5B/6B table.

The 7/8 encoding is considered first, along with a running disparity count. The code is looked up in the 7B/8B table. Then it is optionally inverted if doing so would bring would bring the running disparity closer to 0.

Then the 5/6 encoding is considered. The code is looked up in the code table, and then optionally inverted according to the following rules

1. Attempt to balance the overall 14-bit code.
   1. If the selected 8-bit code has positive disparity, invert the 6-bit code if needed to achieve negative disparity.
   2. If the selected 8-bit code has negative disparity, invert the 6-bit code if needed to achieve positive disparity.
2. Attempt to balance the running disparity
   1. If the selected 8-bit code has even disparity, invert by rules above based on the input running disparity rather than the selected 8-bit code disparity.