Xilinx RocketIO User Manual

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Xilinx RocketIO User Manual Manual pdf 63 page image

RocketIO™ Transceiver User Guide www.xilinx.com 63UG024 (v2.3.2) June 24, 2004 1-800-255-77788B/10B Encoding/Decoding RTXCHARDISPVAL,TXCHARDISPMODETXCHARDISPVAL and TXCHARDISPMODE are dual-purpose ports for the transmitterdepending upon whether 8B/10B encoding is enabled. Table 2-10 shows this dual functionality.When encoding is enabled, these ports function as byte-mapped control ports controlling therunning disparity of the transmitted serial data.In the encoding configuration, the disparity of the serial transmission can be controlled with theTXCHARDISPVAL and TXCHARDISPMODE ports. When TXCHARDISPMODE is set High,the running disparity is set before encoding the specific byte. TXCHARDISPVAL determines if thedisparity is negative (set Low) or positive (set High). Table 2-11 illustrates this.Table 2-10: 8B/10B Bypassed Signal SignificanceFunctionTXBYPASS8B10B 0 8B/10B encoding is enabled (not bypassed). 1, 2, or 4 bits, mapped to number of bytes ofdata path width.1 8B/10B encoding bypassed (disabled). 1, 2, or 4 bits, mapped to number of bytes of datapath width.Function, 8B/10B Enabled Function, 8B/10B BypassedTXCHARDISPMODE,TXCHARDISPVAL 00 Maintain running disparity normally Part of 10-bit encoded byte(see Figure 2-13):TXCHARDISPMODE[0](or: [1] / [2] / [3])TXCHARDISPVAL[0](or: [1] / [2] / [3])TXDATA[7:0](or: [15:8] / [23:16] / [31:24])01 Invert the normally generated runningdisparity before encoding this byte.10 Set negative running disparity beforeencoding this byte.11 Set positive running disparity beforeencoding this byte.RXCHARISK Received byte is a K-character Part of 10-bit encoded byte(see Figure 2-14):RXCHARISK[0](or: [1] / [2] / [3])RXRUNDISP[0](or: [1] / [2] / [3])RXDATA[7:0](or: [15:8] / [23:16] / [31:24])RXRUNDISP0 Indicates running disparity is NEGATIVE1 Indicates running disparity is POSITIVERXDISPERR Disparity error occurred on current byte UnusedTXCHARISK Transmitted byte is a K-character UnusedRXCHARISCOMMA Received byte is a comma Unused