Virtex-4 RocketIO MGT User Guide www.xilinx.com 113UG076 (v4.1) November 2, 20088B/10B Encoding/DecodingRRXCHARISK and RXRUNDISPRXCHARISK and RXRUNDISP are dual-purpose ports for the receiver dependingwhether 8B/10B decoding is enabled. Table 3-6 shows this dual functionality. Whendecoding is enabled, these ports function as byte-mapped status ports of the receiveddata.In the decoding configuration, when RXCHARISK is asserted that byte of the received datais a control (K) character. Otherwise, the received byte of data is a data character. (SeeAppendix B, “8B/10B Valid Characters”). The RXRUNDISP port indicates that thedisparity of the received byte is either negative or positive. RXRUNDISP is asserted toindicate positive disparity. This is used in cases like the “Non-Standard Running DisparityExample,” page 115.In the bypassed configuration, RXCHARISK and RXRUNDISP are additional data bits forthe 10-, 20-, 40-, or 80-bit buses. This is similar to the transmit side. RXCHARISK[0:7]relates to bits 9, 19, 29, 39, 49, 59, 69, and 79 while RXRUNDISP[0:7] pertains to bits 8, 18,28, 38, 48, 58, 68, and 78 of the data bus.RXDISPERRRXDISPERR is a status port for the receiver that is byte-mapped to the RXDATA. When abit is asserted, a disparity error occurred on the received data. This usually indicates thatthe data is corrupt by bit errors, the transmission of an invalid control character, or caseswhen normal disparity is not required, such as shown in the “Non-Standard RunningDisparity Example,” page 115.Table 3-6: 8B/10B Bypassed Signal SignificanceSignalFunctionDecoder Block Enabled Decoder BlockDisabledRXCHARISK Received byte is aK-character. Part of 10-bit encoded byte(see Figure 3-11):RXCHARISK[0],(or: [1]/[2]/[3]/[4]/[5]/[6]/[7])RXRUNDISP[0],(or: [1]/[2]/[3]/[4]/[5]/[6]/[7])RXDATA[7:0](or: [15:8]/[23:16]/[31:24]/[39:32]/[47:40]/[55:48]/[63:56})RXRUNDISP0 Indicates running disparityis NEGATIVE.1 Indicates running disparityis POSITIVE.RXDISPERR Disparity error occurred oncurrent byte. Unused.
