Xilinx 7 Series User Manual

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Xilinx 7 Series User Manual Manual pdf 160 page image

160 www.xilinx.com 7 Series FPGAs GTP Transceivers User GuideUG482 (v1.9) December 19, 2016Chapter 4: Receiverinverted by controlling RXPOLARITY. Otherwise, the PRBS checker does not lock. When it findsthe pattern, it can detect PRBS errors by comparing the incoming pattern with the expected pattern.The expected pattern is generated from the previous incoming data. The checker counts the numberof word (20 bits per word) errors and increments the word error counter by 1 when an error(s) isfound in the incoming parallel data. Thus the word error counter might not match the actual numberof bit errors if the incoming parallel data contains two or more bit errors. The error counter stopscounting when reaching 0xFFFF.When the error occurs, RXPRBSERR is asserted. When no error is found in the following incomingdata, RXPRBSERR is cleared. Asserting RXPRBSCNTRESET clears the error counter.GTRXRESET and RXPCSRESET also reset the count.Refer to TX Pattern Generator, page 103 for more information about use models.RX Byte and Word AlignmentFunctional DescriptionSerial data must be aligned to symbol boundaries before it can be used as parallel data. To makealignment possible, transmitters send a recognizable sequence, usually called a comma. Thereceiver searches for the comma in the incoming data. When it finds a comma, it moves the commato a byte boundary so the received parallel words match the transmitted parallel words.Figure 4-25 shows the alignment to a 10-bit comma. The RX receiving unaligned bits are on theright side. The serial data with the comma is highlighted in the middle. Byte aligned RX parallel datais on the left.X-Ref Target - Figure 4-25Figure 4-25: Conceptual View of Comma Alignment (Aligning to a 10-Bit Comma)1001011000010010011010111001100111001011111001011011001010100100010101010101100110All Subsequent DataAligned to CorrectByte BoundaryAlignment BlockFinds CommaTransmitted FirstUG482_c4_14_110911Stream of Serial DataSend Feedback