Xilinx RocketIO User Manual

Also see for RocketIO: User guide User guide User guide

Contents

Xilinx RocketIO User Manual Manual pdf 66 page image

66 www.xilinx.com RocketIO™ Transceiver User GuideUG024 (v3.0) February 22, 2007Chapter 2: Digital Design ConsiderationsR8B/10B Serial Output FormatThe 8B/10B encoding translates a 8-bit parallel data byte to be transmitted into a 10-bitserial data stream. This conversion and data alignment are shown in Figure 2-15. The serialport transmits the least significant bit of the 10-bit data “a” first and proceeds to “j”. Thisallows data to be read and matched to the form shown in Appendix B, “8B/10B ValidCharacters.”The serial data bit sequence is dependent on the width of the parallel data. The mostsignificant byte is always sent first, regardless of the whether 1-byte, 2-byte, or 4-byte pathsare used. The least significant byte is always last. Figure 2-16 shows a case when the serialdata corresponds to each byte of the parallel data. TXDATA [31:24] is serialized and sentout first, followed by TXDATA [23:16], TXDATA [15:8], and finally TXDATA [7:0]. The2-byte path transmits TXDATA [15:8] and then TXDATA [7:0].HDL Code Examples: Transceiver Bypassing of 8B/10B Encoding8B/10B encoding can be bypassed by the transceiver. The TXBYPASS8B10B is set to 1111;the RXDECODE attribute is set to FALSE to create the extra two bits needed for a 10-bitdata bus; and TXCHARDISPMODE, TXCHARDISPVAL, RXCHARISK, and RXRUNDISPare added to the 8-bit data bus.Please use the Architecture Wizard to create instantiation templates. This wizard createscode and instantiation templates that define the attributes for a specific application.Figure 2-15: 8B/10B Parallel to Serial ConversionFigure 2-16: 4-Byte Serial StructureUG024_10_0211020123457 6ABCDEFH GParallel7 8 9654320 1g h jfiedca bSerial8B/10BFirst transmitted Last transmittedU024_11_020802TXDATA 31:24 TXDATA 23:16 TXDATA 15:8 TXDATA 7:0H3 − A3 H2 − A2 H1 − A1 H0 − A0a3 − j3 a2 − j2 a1 − j1 a0 − j08B/10BLSB3 LSB2 LSB1 LSB01st SentEncoded2nd SentEncoded3rd SentEncoded4th SentEncodedProduct Not Recommended for New Designs