Ports And Attributes; Txbypass8B10B, Rx_Decode_Use - Xilinx RocketIO User Manual

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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
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
If this pair is not matched, the data is not received correctly.
encoding/decoding blocks of the transceiver and how the data passes through these blocks.
Table 2-10
8B/10B is bypassed or enabled.
32/16/8 bits
TXDATA
50 – 156.3 MHz
32/16/8 bits
RXDATA
62
2-10).
shows the significance of 8B/10B ports that change purpose depending on whether
Transceiver Module
Physical Coding Sublayer
F
C
8B/10B
R
F
Encode
C
O
REFCLK
Channel Bonding
and
Clock Correction
CRC
Elastic 8B/10B
Buffer Decode
Figure 2-12: 8B/10B Data Flow
www.xilinx.com
1-800-255-7778
Chapter 2: Digital Design Considerations
Figure 2-12
Physical Media Attachment
Mindspeed IP
I
Serializer
TX Clock Generator
Transmitter
20X Multiplier
Receiver
RX Clock Recovery
Deserializer
Comma Detect
Table 2-10).
shows the
TX+
Transmit
Buffer TX−
Receive
RX+
Buffer
RX−
UG024_09_031203
RocketIO™ Transceiver User Guide
UG024 (v2.3.2) June 24, 2004