Xilinx RocketIO User Manual

66 www.xilinx.com RocketIO™ Transceiver User Guide
UG024 (v3.0) February 22, 2007
Chapter 2: Digital Design Considerations
R
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 Figure 2-15. The serial
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 Appendix B, “8B/10B Valid
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. Figure 2-16 shows a case when the serial
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.
Figure 2-15: 8B/10B Parallel to Serial Conversion
Figure 2-16: 4-Byte Serial Structure
UG024_10_021102
01234576
ABCDEFHG
Parallel
7896543201
ghjfiedcab
Serial
8B/10B
First transmitted Last transmitted
U024_11_020802
TXDATA 31:24 TXDATA 23:16 TXDATA 15:8 TXDATA 7:0
H
3
− A
3
H
2
− A
2
H
1
− A
1
H
0
− A
0
a
3
− j
3
a
2
− j
2
a
1
− j
1
a
0
− j
0
8B/10B
LSB
3
LSB
2
LSB
1
LSB
0
1
st
Sent
Encoded
2
nd
Sent
Encoded
3
rd
Sent
Encoded
4
th
Sent
Encoded
Product Not Recommended for New Designs

Xilinx RocketIO Specifications

General

Brand	Xilinx
Model	RocketIO
Category	Transceiver
Language	English