Xilinx RocketIO User Manual

RocketIO™ Transceiver User Guide www.xilinx.com 63
UG024 (v3.0) February 22, 2007
8B/10B Encoding/Decoding
R
When TXCHARDISPMODE is set Low, the running disparity is maintained if
TXCHARDISPVAL is also set Low, but the disparity is inverted before encoding the byte
when TXCAHRDISPVAL is set High.
Most applications will use the mode where both TXCHARDISPMODE and
TXCHARDISPVAL are set Low. Some applications may use other settings if special
running disparity configurations are required, such as in the “Vitesse Disparity Example”
below.
In the bypassed configuration, TXCHARDISPMODE [0] becomes bit 9 of the 10 bits of
encoded data. TXCHARDISPMODE [1:3] are bits 19, 29, and 39 in the 20- and 40-bit wide
buses. TXCHARDISPVAL becomes bits 8, 18, 28, and 38 of the transmit data. See
Figure 2-13.
TXCHARISK
TXCHARISK is a byte-mapped control port that is used only when the 8B/10B encoder is
implemented. This port controls whether the byte of TXDATA is to be encoded as a control
(K) character (when asserted High) or as a data character (when de-asserted). When
8B/10B encoding is bypassed, this port is undefined.
TXRUNDISP
TXRUNDISP is a status port that is byte-mapped to TXDATA. This port indicates the
running disparity after the byte of TXDATA is encoded. When High, the disparity is
positive. When Low, the disparity is negative.
TXKERR
TXKERR is a status port that is byte-mapped to TXDATA. This port is defined only if
8B/10B encoding is enabled. If a bit is asserted High, it means that TXDATA and
TXCHARISK have combined to create an invalid control (K) character. The transmission,
reception, and decode of this invalid character will create unexpected RXDATA results in
the RocketIO receiver, or in other transceivers.
RXCHARISK,
RXRUNDISP
RXCHARISK and RXRUNDISP are dual-purpose ports for the receiver depending
whether 8B/10B decoding is enabled. Table 2-10 shows this dual functionality. When
decoding is enabled, the ports function as byte-mapped status ports for the received data.
Table 2-11: Running Disparity Control
{TXCHARDISPMODE,
TXCHARDISPVAL}
Function
00 Maintain running disparity normally
01
Invert normally generated running disparity before
encoding this byte
10 Set negative running disparity before encoding this byte
11 Set positive running disparity before encoding this byte
Product Not Recommended for New Designs

Xilinx RocketIO Specifications

General

Brand	Xilinx
Model	RocketIO
Category	Transceiver
Language	English