8B/10B Serial Output Format; Hdl Code Examples: Transceiver Bypassing Of 8B/10B Encoding - Xilinx RocketIO User Manual

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8B/10B Serial Output Format

The 8B/10B encoding translates a 8-bit parallel data byte to be transmitted into a 10-bit
serial data stream. This conversion and data alignment are shown in
port transmits the least significant bit of the 10-bit data "a" first and proceeds to "j". This
allows data to be read and matched to the form shown in
Characters."
The serial data bit sequence is dependent on the width of the parallel data. The most
significant byte is always sent first, regardless of the whether 1-byte, 2-byte, or 4-byte paths
are used. The least significant byte is always last.
data corresponds to each byte of the parallel data. TXDATA [31:24] is serialized and sent
out first, followed by TXDATA [23:16], TXDATA [15:8], and finally TXDATA [7:0]. The
2-byte path transmits TXDATA [15:8] and then TXDATA [7:0].

HDL Code Examples: Transceiver Bypassing of 8B/10B Encoding

8B/10B encoding can be bypassed by the transceiver. The TXBYPASS8B10B is set to 1111;
the RXDECODE attribute is set to FALSE to create the extra two bits needed for a 10-bit
data bus; and TXCHARDISPMODE, TXCHARDISPVAL, RXCHARISK, and RXRUNDISP
are added to the 8-bit data bus.
Please use the Architecture Wizard to create instantiation templates. This wizard creates
code and instantiation templates that define the attributes for a specific application.
66
H G F
7 6 5
Parallel
a b c
0 1 2
Serial
First transmitted
Figure 2-15: 8B/10B Parallel to Serial Conversion
H 3 − A 3 H 2 − A 2
TXDATA 31:24 TXDATA 23:16
a 3 − j 3 a 2 − j 2
LSB 3 LSB 2
1 st Sent 2 nd Sent
Encoded Encoded
Figure 2-16: 4-Byte Serial Structure
www.xilinx.com
Chapter 2: Digital Design Considerations
Appendix B, "8B/10B Valid
E D C B A
4 3 2 1 0
8B/10B
d e i f g h
3 4 5 6 7 8
Last transmitted
UG024_10_021102
Figure 2-16 shows a case when the serial
H 1 − A 1 H 0 − A 0
TXDATA 15:8 TXDATA 7:0
8B/10B
a 1 − j 1 a 0 − j 0
LSB 1 LSB 0
3 rd Sent 4 th Sent
Encoded Encoded
RocketIO™ Transceiver User Guide
UG024 (v3.0) February 22, 2007
Figure 2-15. The serial
j
9
U024_11_020802