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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
. 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
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.
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
0
1
2
3
4
5
7
6
A
B
C
D
E
F
H
G
Parallel
7
8
9
6
5
4
3
2
0
1
g
h
j
f
i
e
d
c
a
b
Serial
8B/10B
First transmitted
Last transmitted
U024_11_020802
TXDATA 31:24
TXDATA 23:16
TXDATA 15:8
TXDATA 7:0
H3
−
A3
H2
−
A2
H1
−
A1
H0
−
A0
a3
−
j3
a2
−
j2
a1
−
j1
a0
−
j0
8B/10B
LSB3
LSB2
LSB1
LSB0
1st Sent
Encoded
2nd Sent
Encoded
3rd Sent
Encoded
4th Sent
Encoded
Product Not Recommended for New Designs