8-Bit / 10-Bit Alignment; 10-Bit Alignment For 8B/10B Encoded Data - Xilinx Virtex-4 RocketIO User Manual

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8-Bit / 10-Bit Alignment

The MCOMMA_32B_VALUE, PCOMMA_32B_VALUE, COMMA_10B_MASK, and
COMMA32 attributes determine the symbols the comma detection block uses to align
data. After it is configured, the comma detection block searches the data stream for these
symbols. When a symbol is found, the incoming data is shifted so the symbol is aligned
with a byte boundary. Virtex-4 users should note that the 10-bit values (for example, as
used in the 8B/10B encoding scheme) are reversed relative to Virtex-II Pro devices, but are
similar to Virtex-II Pro X devices. For other generation differences, see
"Virtex-II Pro/Virtex-II Pro X to Virtex-4 RocketIO Transceiver Design Migration."

10-Bit Alignment for 8B/10B Encoded Data

Figure 3-12
attributes MCOMMA_32B_VALUE and PCOMMA_32B_VALUE, as well as the attributes
MCOMMA_DETECT, PCOMMA_DETECT, and COMMA_10B_MASK, can be used to
define two symbols of up to 10 bits.
For 10-bit alignment (as in 8B/10B encoding), the attribute COMMA32 must be set to
FALSE.
The comma alignment block can be configured to notify the application when a comma is
detected. If MCOMMA_DETECT is TRUE, RXCOMMADET is set to logic 1 when an
MCOMMA is detected; when PCOMMA_DETECT is TRUE, RXCOMMADET is set to
logic 1 when a PCOMMA is detected. See
ENPCOMMAALIGN and ENMCOMMAALIGN can be driven Low to turn off alignment
and keep the current alignment position.
Note that RXCOMMADET is a signal that is not byte-aligned. Additionally, it is generated
on RXUSRCLK, so its width is always one RXUSRCLK.
Virtex-4 RocketIO MGT User Guide
UG076 (v4.1) November 2, 2008
shows an example of Virtex-4 10-bit comma detection. The lower 10 bits of the
Bit N-1
(N= Word Length)
Received Last
1 0 1 0 1 1 1 0 0 0 1 0 1 0 1 1 1 1 1 0 0 1 1 1 0 1 0 1 1 1 0 1
Note: Reversal
relative to 8B/10B
tables (K28.5 shown)
Figure 3-12: 8B/10B Comma Detection Example
www.xilinx.com
Symbol Alignment and Detection (Comma Detection)
0 1 0 1 1 1 1 1 0 0
j h g f i e d c b a
Bit 9 Bit 0
0 0 0 1 1 1 1 1 1 1
Bit 9 Bit 0
Table 3-9. After successful alignment,
Appendix E,
Bit 0
Received First
MCOMMA_32B_VALUE[9:0]
or
PCOMMA_32B_VALUE[9:0]
COMMA_10B_MASK[9:0]
UG035_CH2_12_050906
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