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Configurable 8B/10B Decoder
Overview
Many protocols require receivers to decode 8B/10B data. 8B/10B is an industry standard
encoding scheme that trades two bits of overhead per byte for improved performance.
Table 6-3, page 98
8B/10B maps 10-bit sequences to 8-bit data and control values.
The GTP transceiver includes an 8B/10B decoder to decode RX data without consuming
FPGA resources. The decoder includes status signals to indicate errors and incoming
control sequences. If decoding is not needed, the block can be disabled to minimize latency.
Ports and Attributes
Table 7-24
Table 7-24: RX Decoder Ports
Port
RXCHARISCOMMA0[1:0]
RXCHARISCOMMA1[1:0]
RXCHARISK0[1:0]
RXCHARISK1[1:0]
RXDEC8B10BUSE0
RXDEC8B10BUSE1
RXDISPERR0[1:0]
RXDISPERR1[1:0]
RXNOTINTABLE0[1:0]
RXNOTINTABLE1[1:0]
RXRUNDISP0[1:0]
RXRUNDISP1[1:0]
Virtex-5 RocketIO GTP Transceiver User Guide
UG196 (v1.3) May 25, 2007
outlines the benefits and costs of 8B/10B.
defines the RX decoder ports.
Dir Clock Domain
RXCHARISCOMMA is asserted when RXDATA is an 8B/10B
comma. This signal, which depends on DEC_MCOMMA_DETECT
and DEC_PCOMMA_DETECT, is always Low when
RXDEC8B10BUSE is Low.
Out
RXUSRCLK2
RXCHARISCOMMA is a two-bit signal. Bit 0 corresponds to the
lower byte of RXDATA, and bit 1 corresponds to the upper byte.
When RXDATAWIDTH = 0 (one-byte interface), only bit 0 is used.
RXCHARISK is asserted when RXDATA is an 8B/10B K character.
This signal is always Low when RXDEC8B10BUSE is Low.
Out
RXUSRCLK2
RXCHARISK is a two-bit signal. Bit 0 corresponds to the lower byte
of RXDATA, and bit 1 corresponds to the upper byte. When
RXDATAWIDTH = 0 (one-byte interface), only bit 0 is used.
RXDEC8B10BUSE enables the 8B/10B decoder.
In
RXUSRCLK2
1: 8B/10B decoder enabled
0: 8B/10B decoder bypassed (reduces latency)
When High, RXDISPERR indicates that RXDATA was received
with a disparity error.
Out
RXUSRCLK2
RXDISPERR is a two-bit signal. Bit 0 corresponds to the lower byte
of RXDATA, and bit 1 corresponds to the upper byte. When
RXDATAWIDTH = 0 (one-byte interface), only bit 0 is used.
RXNOTINTABLE indicates that RXDATA is the result of an illegal
8B/10B code and is in error.
Out
RXUSRCLK2
RXNOTINTABLE is a two-bit signal. Bit 0 corresponds to the lower
byte of RXDATA, and bit 1 corresponds to the upper byte. When
RXDATAWIDTH = 0 (one-byte interface), only bit 0 is used.
RXRUNDISP shows the running disparity of the 8B/10B encoder
when RXDATA is received.
Out
RXUSRCLK2
RXRUNDISP is a two-bit signal. Bit 0 corresponds to the lower byte
of RXDATA, and bit 1 corresponds to the upper byte. When
RXDATAWIDTH = 0 (one-byte interface), only bit 0 is used.
www.xilinx.com
Configurable 8B/10B Decoder
Appendix C
shows how
Description
157
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