Virtex-4 RocketIO MGT User Guide www.xilinx.com 105UG076 (v4.1) November 2, 2008Bus InterfaceRFabric Interface FunctionalityThe number of RXUSRCLK2 cycles required to read RXDATA varies depending on theinterface mode (width). The MGT's internal datapath is 4 bytes wide; therefore, in 2-byte or1-byte mode, "future" information is overloaded onto the unused bytes. Table 3-3summarizes this operation of the fabric interface. Figure 3-5 illustrates the operationgraphically, as a user might view it at the ports of the MGT.Table 3-3: Fabric Interface FunctionalityRXUSRCLK2CycleInterface Mode (Width)8-Byte 4-Byte(1) 2-Byte(2) 1-Byte(3)Cycle 0 RXDATA[63:0] 32'h00000000,RXDATA[31:0]32'h00000000,RXDATA[31:16],RXDATA[15:0]32'h00000000,RXDATA[31:24],RXDATA[23:16],RXDATA[15:8],RXDATA[7:0]Cycle 1 Same as Cycle 0 Same as Cycle 032'h00000000,16’h0000,RXDATA[31:16]32'h00000000,8’h00,RXDATA[31:24],RXDATA[23:16],RXDATA[15:8]Cycle 2 Same as Cycle 0 Same as Cycle 0 Same as Cycle 032'h00000000,8’h00,8’h00,RXDATA[31:24],RXDATA[23:16]Cycle 3 Same as Cycle 0 Same as Cycle 0 Same as Cycle 132'h00000000,8’h00,8’h00,8’h00,RXDATA[31:24]Cycle 4 Same as Cycle 0 Same as Cycle 0 Same as Cycle 0 Same as Cycle 0Cycle 5 Same as Cycle 0 Same as Cycle 0 Same as Cycle 1 Same as Cycle 1Cycle 6 Same as Cycle 0 Same as Cycle 0 Same as Cycle 0 Same as Cycle 2Cycle 7 Same as Cycle 0 Same as Cycle 0 Same as Cycle 1 Same as Cycle 3Notes:1. User accesses lower 4 bytes.2. User accesses lower 2 bytes.3. User accesses lower 1 byte
