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Chapter 7: GTP Receiver (RX)
Table 7-25
Table 7-25: RX Decoder Attributes
Attributes
DEC_MCOMMA_DETECT_0
DEC_MCOMMA_DETECT_1
DEC_PCOMMA_DETECT_0
DEC_PCOMMA_DETECT_1
DEC_VALID_COMMA_ONLY_0
DEC_VALID_COMMA_ONLY_1
Description
Enabling the 8B/10B Decoder
To disable the 8B/10B decoder, RXDEC8B10BUSE is driven Low. With the decoder off, the
number of bits per byte on the RX interface is determined by the internal data width of the
tile. See
parallel bitmapping when 8B/10B decoding is bypassed.
To enable the 8B/10B decoder, RXDEC8B10BUSE is driven High. INTDATAPATH must
also be High (10-bit internal datapath) to enable the 8B/10B decoder because it requires
10-bit wide data.
8B/10B Decoder Bit and Byte Order
The order of the bits into the 8B/10B decoder is the opposite of the order shown in the
8B/10B table in
transceiver always receives the right-most bit first. Consequently, the 8B/10B decoder is
designed to automatically reverse the bit order of received data before decoding it.
Similarly, because the GTP transceiver receives the right-most bit first, when a two-byte
interface is used, the first byte received (byte 0) is presented on RXDATA[7:0], and the
second byte is presented on RXDATA[15:8].
10-bit data to 8-bit values.
158
defines the RX decoder attributes.
Enables detection of negative 8B/10B commas:
TRUE: RXCHARISCOMMA is asserted when RXDATA is a negative 8B/10B
comma
FALSE: RXCHARISCOMMA does not respond to negative 8B/10B commas
Enables detection of positive 8B/10B commas:
TRUE: RXCHARISCOMMA is asserted when RXDATA is a positive 8B/10B
comma
FALSE: RXCHARISCOMMA does not respond to positive 8B/10B commas
Limits the set of commas to which RXCHARISCOMMA responds.
TRUE: RXCHARISCOMMA is asserted only for K28.1, K28.5, and K28.7 (see
8B/10B K character table in Appendix C)
FALSE: RXCHARISCOMMA responds to any positive or negative 8B/10B
comma, depending on the settings for DEC_MCOMMA_DETECT and
DEC_PCOMMA_DETECT
"FPGA RX Interface," page 182
Appendix
C. 8B/10B requires bit a0 to be received first, but the GTP
www.xilinx.com
Description
for details about the deserialization order and
Figure 7-18
shows how the decoder maps
Virtex-5 RocketIO GTP Transceiver User Guide
UG196 (v1.3) May 25, 2007
R
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