
A–2 Altera Corporation
Stratix GX Transceiver User Guide January 2005
8B/10B Code
Figure A–2. 10-Bit Grouping of 6-Bit & 4-Bit Sub-Blocks
The running disparity at the beginning of the 6-bit sub-block is the
running disparity at the end of the previous 10-bit code. The running
disparity of the 4-bit sub-block is the running disparity of the end of the
6-bit sub-block. The running disparity of the end of the 4-bit sub-block is
the running disparity of the 10-bit code, as shown in Figure A–3.
Figure A–3. Running Disparity Between Sub-Blocks
The running disparity calculation rules are as follows (if the conditions
are not met, then the running disparity at the end of the sub-blocks are the
same as the beginning of the sub-block):
■ The current running disparity at the end of a sub-block is positive if
any of the following are true:
● The sub-block contains more ones than zeros.
● The 6-bit sub-block is 6'b000111.
● The 4-bit sub-block is 4'b0011.
■ The current running disparity at the end of a sub-block is negative if
any of the following are true:
● The sub-block contains more zeros than ones.
● The 6-bit sub-block is 6'b111000.
● The 4-bit sub-block is 4'b1100.
7 6 5 4 3 2 1 09 8
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6-Bit Block4-Bit Block
10-Bit Code
0 0 0 1 1 1 0 00 1
6-Bit Block4-Bit Block
10-Bit Code
0 0 1 1 0 1 0 11 1
6-Bit Block4-Bit Block
10-Bit Code
RD+
RD+
RD+
RD-
1st Bit
Receive
Last Bit
Received
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