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.

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.

Also like 8B/10B, a running disparity is output with each code, and fed back to the input for use in selecting the next code.

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. Some codes naturally have 0 disparity (4 ones and 4 zeros), and these are never inverted.

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

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.
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.

K-Codes

There are 9 Control Codes (K-Codes) which are considered separately from the 7/8-5/6 encoding algorithm. If the dataKIn input is high, then the 14-bit output is selected from the table below.

The normal output (Out 14b) is selected when the input disparity is -2. Otherwise the inverted output is selected. Control codes may get inverted even if their encoded disparity is 0.

K.120.3, K.120.11 and K.120.19 are special COMMA codes that can be used to perform word alignment on encoded serial streams. These codes contain an internal run of 7 consecutive 1's (or 0's when inverted). Such a run will never be seen for any other combination of codes in the output stream.

If dataKIn is high and the input code is not in the table, then the output is indeterminant.

Name	In 12b	Out 14b	Out Disp	Notes
K.120.0	`000001111000`	`00011011111000`	0
K.120.1	`000011111000`	`01000111111000`	0
K.120.2	`000101111000`	`01001011111000`	0
K.120.3	`000111111000`	`10001111111000`	+2	COMMA
K.120.4	`001001111000`	`01010011111000`	0
K.120.7	`001111111000`	`11100011111000`	+2
K.120.8	`010001111000`	`01100011111000`	0
K.120.11	`010111111000`	`00101111111000`	+2	COMMA
K.120.16	`100001111000`	`00100111111000`	0
K.120.19	`100111111000`	`01001111111000`	+2	COMMA
K.120.23	`101111111000`	`10100011111000`	0
K.120.24	`110001111000`	`00110011111000`	0
K.120.27	`110111111000`	`10010011111000`	0
K.120.29	`111011111000`	`10001011111000`	0
K.120.30	`111101111000`	`10000111111000`	0
K.120.31	`111111111000`	`00101011111000`	0

SSP

The SLAC Streaming Protocol (SSP) 12b/14b implementation uses K.120.11 for IDLE (and alignment), K.120.0 for Start-of-Frame (SOF) and K.120.1 for End-of-Frame (EOF).

7B/8B Code Table

Name	In 7b	Out 8b	Out Disparity	Alt 8b	Alt Disparity
D.0	0000000	01011000	-2	10100111	2
D.1	0000001	00011001	-2	11100110	2
D.2	0000010	00011010	-2	11100101	2
D.3	0000011	00100011	-2	11011100	2
D.4	0000100	01100100	-2	10011011	2
D.5	0000101	10000101	-2	01111010	2
D.6	0000110	10000110	-2	01111001	2
D.7	0000111	10000111	0	#N/A	0
D.8	0001000	01101000	-2	10010111	2
D.9	0001001	10001001	-2	01110110	2
D.10	0001010	01001010	-2	10110101	2
D.11	0001011	10001011	0	#N/A	0
D.12	0001100	01001100	-2	10110011	2
D.13	0001101	10001101	0	#N/A	0
D.14	0001110	10001110	0	#N/A	0
D.15	0001111	11000111	2	00111000	-2
D.16	0010000	00010011	-2	11101100	2
D.17	0010001	10010001	-2	01101110	2
D.18	0010010	10010010	-2	01101101	2
D.19	0010011	10010011	0	#N/A	0
D.20	0010100	10010100	-2	01101011	2
D.21	0010101	10010101	0	#N/A	0
D.22	0010110	10010110	0	#N/A	0
D.23	0010111	00010111	0	#N/A	0
D.24	0011000	10011000	-2	01100111	2
D.25	0011001	10011001	0	#N/A	0
D.26	0011010	10011010	0	#N/A	0
D.27	0011011	00011011	0	#N/A	0
D.28	0011100	10011100	0	#N/A	0
D.29	0011101	00011101	0	#N/A	0
D.30	0011110	00011110	0	#N/A	0
D.31	0011111	00011100	-2	11100011	2
D.32	0100000	00100101	-2	11011010	2
D.33	0100001	10100001	-2	01011110	2
D.34	0100010	00100110	-2	11011001	2
D.35	0100011	10100011	0	#N/A	0
D.36	0100100	10100100	-2	01011011	2
D.37	0100101	10100101	0	#N/A	0
D.38	0100110	10100110	0	#N/A	0
D.39	0100111	00100111	0	#N/A	0
D.40	0101000	00101001	-2	11010110	2
D.41	0101001	10101001	0	#N/A	0
D.42	0101010	10101010	0	#N/A	0
D.43	0101011	00101011	0	#N/A	0
D.44	0101100	10101100	0	#N/A	0
D.45	0101101	00101101	0	#N/A	0
D.46	0101110	00101110	0	#N/A	0
D.47	0101111	00101010	-2	11010101	2
D.48	0110000	00110010	-2	11001101	2
D.49	0110001	10110001	0	#N/A	0
D.50	0110010	10110010	0	#N/A	0
D.51	0110011	00110011	0	#N/A	0
D.52	0110100	10110100	0	#N/A	0
D.53	0110101	00110101	0	#N/A	0
D.54	0110110	00110110	0	#N/A	0
D.55	0110111	00110111	2	11001000	-2
K.55	0110111	10110111	4	01001000	-4
D.56	0111000	10111000	0	#N/A	0
D.57	0111001	00111001	0	#N/A	0
K.57	0111001	10111001	2	01000110	-2
D.58	0111010	00111010	0	#N/A	0
D.59	0111011	00111011	2	11000100	-2
D.60	0111100	00111100	0	#N/A	0
D.61	0111101	10111101	4	01000010	-4
D.62	0111110	00110100	-2	11001011	2
D.63	0111111	10111011	4	01000100	-4
D.64	1000000	01010100	-2	10101011	2
D.65	1000001	11000001	-2	00111110	2
D.66	1000010	11000010	-2	00111101	2
D.67	1000011	11000011	0	#N/A	0
D.68	1000100	01000001	-4	10111110	4
D.69	1000101	11000101	0	#N/A	0
D.70	1000110	11000110	0	#N/A	0
D.71	1000111	01000111	0	#N/A	0
D.72	1001000	01001001	-2	10110110	2
D.73	1001001	11001001	0	#N/A	0
D.74	1001010	11001010	0	#N/A	0
D.75	1001011	01001011	0	#N/A	0
D.76	1001100	11001100	0	#N/A	0
D.77	1001101	01001101	0	#N/A	0
D.78	1001110	01001110	0	#N/A	0
D.79	1001111	01000101	-2	10111010	2
D.80	1010000	01000011	-2	10111100	2
D.81	1010001	11010001	0	#N/A	0
D.82	1010010	11010010	0	#N/A	0
D.83	1010011	01010011	0	#N/A	0
D.84	1010100	11010100	0	#N/A	0
D.85	1010101	01010101	0	#N/A	0
D.86	1010110	01010110	0	#N/A	0
D.87	1010111	01010111	2	10101000	-2
D.88	1011000	11011000	0	#N/A	0
D.89	1011001	01011001	0	#N/A	0
D.90	1011010	01011010	0	#N/A	0
D.91	1011011	11010011	2	00101100	-2
D.92	1011100	01011100	0	#N/A	0
D.93	1011101	01011101	2	10100010	-2
D.94	1011110	11001110	2	00110001	-2
D.95	1011111	11011110	4	00100001	-4
D.96	1100000	01100010	-2	10011101	2
D.97	1100001	11100001	0	#N/A	0
D.98	1100010	11100010	0	#N/A	0
D.99	1100011	01100011	0	#N/A	0
D.100	1100100	11100100	0	#N/A	0
D.101	1100101	01100101	0	#N/A	0
D.102	1100110	01100110	0	#N/A	0
D.103	1100111	11100111	4	00011000	-4
D.104	1101000	11101000	0	#N/A	0
D.105	1101001	01101001	0	#N/A	0
D.106	1101010	01101010	0	#N/A	0
D.107	1101011	11101011	4	00010100	-4
D.108	1101100	01101100	0	#N/A	0
D.109	1101101	11101001	2	00010110	-2
D.110	1101110	11101010	2	00010101	-2
D.111	1101111	11101101	4	00010010	-4
D.112	1110000	00100100	-4	11011011	4
D.113	1110001	01110001	0	#N/A	0
D.114	1110010	01110010	0	#N/A	0
D.115	1110011	01010001	-2	10101110	2
D.116	1110100	01110100	0	#N/A	0
D.117	1110101	01110101	2	10001010	-2
D.118	1110110	01010010	-2	10101101	2
D.119	1110111	01110111	4	10001000	-4
K.120	1111000	11111000	2	00000111	-2
D.120	1111000	01111000	0	#N/A	0
D.121	1111001	01100001	-2	10011110	2
D.122	1111010	01111011	4	10000100	-4
D.123	1111011	01110011	2	10001100	-2
D.124	1111100	01111100	2	10000011	-2
D.125	1111101	01111101	4	10000010	-4
D.126	1111110	01111110	4	10000001	-4
D.127	1111111	11101110	4	00010001	-4

5B/6B Code Table

Name	In 5b	Out 6b	Out Disparity	Alt 6b	Alt Disparity
D.x.0	00000	000110	-2	111001	2
D.x.1	00001	010001	-2	101110	2
D.x.2	00010	010010	-2	101101	2
D.x.3	00011	100011	0	NA	NA
D.x.4	00100	010100	-2	101011	2
D.x.5	00101	100101	0	NA	NA
D.x.6	00110	100110	0	NA	NA
D.x.7	00111	000111	0	NA	NA
D.x.8	01000	011000	-2	100111	2
D.x.9	01001	101001	0	NA	NA
D.x.10	01010	101010	0	NA	NA
D.x.11	01011	001011	0	NA	NA
D.x.12	01100	101100	0	NA	NA
D.x.13	01101	001101	0	NA	NA
D.x.14	01110	001110	0	NA	NA
D.x.15	01111	000101	-2	111010	2
K.x.28	11100	111100	2	000011	-2
D.x.16	10000	110110	2	001001	-2
D.x.17	10001	110001	0	NA	NA
D.x.18	10010	110010	0	NA	NA
D.x.19	10011	010011	0	NA	NA
D.x.20	10100	110100	0	NA	NA
D.x.21	10101	010101	0	NA	NA
D.x.22	10110	010110	0	NA	NA
D.x.23	10111	010111	2	101000	-2
D.x.24	11000	001100	-2	110011	2
D.x.25	11001	011001	0	NA	NA
D.x.26	11010	011010	0	NA	NA
D.x.27	11011	011011	2	100100	-2
D.x.28	11100	011100	0	NA	NA
D.x.29	11101	011101	2	100010	-2
D.x.30	11110	011110	2	100001	-2
D.x.31	11111	110101	2	001010	-2

Contact

Ben Reese

bareese@slac.stanford.edu

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