Xilinx Virtex-6 FPGA User Manual

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Xilinx Virtex-6 FPGA User Manual Manual pdf 219 page image

Virtex-6 FPGA GTX Transceivers User Guide www.xilinx.com 219UG366 (v2.5) January 17, 2011RX Byte and Word Alignmenton RX_DATA_WIDTH. Either a 16-bit or a 20-bit comma alignment mode is possible.Figure 4-24 shows how the commas are combined when COMMA_DOUBLE is TRUE.Figure 4-25 shows how COMMA_10B_ENABLE and wildcarding work for a double-widthcomma.Activating Comma AlignmentCommas are aligned to the closest boundary providing they are found while commaalignment is active. RXENMCOMMAALIGN is driven High to align on the MCOMMApattern. RXENPCOMMAALIGN is driven High to activate alignment on the PCOMMApattern. Both enable ports are driven to align to either pattern. When COMMA_DOUBLEis TRUE, both enable ports must always be driven to the same value.Alignment Status SignalsWhile MCOMMA or PCOMMA alignment is active, any matching comma pattern causesthe block to realign to the closest boundary. After successful alignment, the block holdsRXBYTEISALIGNED High. At this time, RXENMCOMMAALIGN andRXENPCOMMAALIGN can be driven Low to turn off alignment and keep the currentalignment position. PCOMMA_DETECT must be TRUE for PCOMMAs to causeRXBYTEISALIGNED to go High. Similarly, MCOMMA_DETECT must be TRUE forMCOMMAs to cause RXBYTEISALIGNED to go High. Commas can arrive whileRXBYTEISALIGNED is High. If the commas arrive aligned to boundaries, there is nochange. If the commas arrive out of position, the block deasserts RXBYTEISALIGNEDuntil the commas are aligned again. If alignment is still activated for the comma thatarrives, the block automatically aligns the new comma to the closest boundary and drivesRXBYTEREALIGN High for one RXUSRCLK2 cycle.X-Ref Target - Figure 4-24Figure 4-24: Extended Comma Pattern DefinitionX-Ref Target - Figure 4-25Figure 4-25: Extended Comma Pattern MaskingMCOMMA_10B_VALUE PCOMMA_10B_VALUEUG366_c4_22_0515090010100010xx1010000100111111110010100001xx1010001000111111110011111111MCOMMA_10B_VALUEandPCOMMA_10B_VALUE(COMMA_DOUBLE = TRUE) Pattern requiredfor comma detection(x = don’t care)COMMA_10B_ENABLE UG366_c4_23_051509www.BDTIC.com/XILINX