Encoder - Xilinx Virtex-4 RocketIO User Manual

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Encoder

A bypassable 8B/10B encoder is included in the transmitter. The encoder uses the same
256 data characters and 12 control characters (shown in
Characters") that are used for Gigabit Ethernet, XAUI, Fibre Channel, and InfiniBand.
The encoder accepts 8 bits of data along with a K-character signal for a total of 9 bits per
character applied. If the K-character signal is set to a logic 1, the data is encoded into one of
the 12 possible K-characters available in the 8B/10B code. If the K-character input is set to
a logic 0, the 8 bits are encoded as standard data.
There are two ports that enable the 8B/10B encoding in the transceiver:
•
•
Virtex-4 RocketIO MGT User Guide
UG076 (v4.1) November 2, 2008
TXENC8B10BUSE controls whether the 8B/10B encoding block is used or not. When
set to logic 1, the 8B/10B encoding block is used. When set to logic 0, the 8B/10B
encoding block is not used, allowing complete encoding bypass. See
Applications wanting a direct 10-bit interface to the MGT supply the extra bits on the
TXCHARDISPMODE and TXCHARDISPVAL buses. Refer
TXBYPASS8B10B is a byte-mapped port that is 1, 2, 4 or 8 bits wide depending on the
data width of the transceiver primitive being used. These bits correlate to each byte of
the data path. This signal allows the data to bypass the 8B/10B encoding of the
transmitter on a clock-by-clock basis. When set to a logic 1, the 8B/10B encoding is
bypassed. In this mode, the extra bits are fed through the TXCHARDISPMODE and
TXCHARDISPVAL buses. Otherwise, the normal 8-, 16-, 32-, or 64-bit fabric interfaces
are used. Note that running disparity is not synchronized with the encoder when this
bypass is asserted. This feature should be used only by applications that are not
interested in tracking disparity errors.
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8B/10B Encoding/Decoding
Appendix B, "8B/10B Valid
Table 3-4.
toFigure 3-10.
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