Xilinx RocketIO User Manual

RocketIO™ Transceiver User Guide www.xilinx.com 61
UG024 (v3.0) February 22, 2007
8B/10B Encoding/Decoding
R
Ports and Attributes
TXBYPASS8B10B,
RX_DECODE_USE
One port and one attribute enable 8B/10B encoding/decoding in the transceiver.
TXBYPASS8B10B is a byte-mapped port that is 1, 2, or 4 bits wide, depending on the data
width of the transceiver primitive being used. These bits correlate to each byte of the data
path. To enable 8B/10B encoding in the transmitter, these bits must be set Low. In this
mode, the transmit data input to the TXDATA port is non-encoded data of either 8, 16, or
32 bits wide. However, if other encoding schemes are preferred, the encoder capabilities
can be bypassed by setting all bits High. In this mode, the data input to TXDATA is either
10, 20, or 40 bits wide. The extra bits are fed through the TXCHARDISPMODE and
TXCHARDISPVAL buses (shown in Table 2-10).
The decoder is controlled by the attribute RX_DECODE_USE. When this attribute is set to
TRUE, the decoder is enabled and should coincide with TXBYPASS8B10B being set Low. In
this mode, the received data output from the RXDATA port is decoded data, either 8, 16, or
32 bits wide. However, when the attribute is set to FALSE, the decoder is disabled. In this
mode, the received data is 10, 20, or 40 bits wide, and the extra bits are provided by
RXCHARISK and RXRUNDISP (shown in Table 2-10).
If this pair is not matched, the data is not received correctly. Figure 2-12 shows the
encoding/decoding blocks of the transceiver and how the data passes through these
blocks. Table 2-10 shows the significance of 8B/10B ports that change purpose depending
on whether 8B/10B is bypassed or enabled.
Figure 2-12: 8B/10B Data Flow
UG024_09_020507
TX+
TX−
RX+
RX−
Channel Bonding
and
Clock Correction
TX Clock Generator
RX Clock Recovery
REFCLK
Deserializer
Serializer
Transmit
Buffer
Transmitter
Receiver
Transceiver Module
32/16/8 bits
32/16/8 bits
50 – 156.3 MHz
8B/10B
Encode
Elastic
Buffer
Receive
Buffer
20X Multiplier
Physical Coding Sublayer Physical Media Attachment
Mindspeed IP
CRC
C
R
C
F
I
F
O
8B/10B
Decode
RXDATA
Loop-back
Loop-back (parallel)
TXDATA
Comma Detect
Product Not Recommended for New Designs

Xilinx RocketIO Specifications

General

Brand	Xilinx
Model	RocketIO
Category	Transceiver
Language	English