Rx Byte And Word Alignment - Xilinx 7 Series User Manual

Chapter 4: Receiver
inverted by controlling RXPOLARITY. Otherwise, the PRBS checker does not lock. When it finds
the 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 number
of word (20 bits per word) errors and increments the word error counter by 1 when an error(s) is
found in the incoming parallel data. Thus the word error counter might not match the actual number
of bit errors if the incoming parallel data contains two or more bit errors. The error counter stops
counting when reaching 0xFFFF.
When the error occurs, RXPRBSERR is asserted. When no error is found in the following incoming
data, RXPRBSERR is cleared. Asserting RXPRBSCNTRESET clears the error counter.
GTRXRESET and RXPCSRESET also reset the count.
Refer to

RX Byte and Word Alignment

Functional Description
Serial data must be aligned to symbol boundaries before it can be used as parallel data. To make
alignment possible, transmitters send a recognizable sequence, usually called a comma. The
receiver searches for the comma in the incoming data. When it finds a comma, it moves the comma
to a byte boundary so the received parallel words match the transmitted parallel words.
Figure 4-25
right side. The serial data with the comma is highlighted in the middle. Byte aligned RX parallel data
is on the left.
X-Ref Target - Figure 4-25
Figure 4-25: Conceptual View of Comma Alignment (Aligning to a 10-Bit Comma)
160
Send Feedback
TX Pattern Generator, page 103
shows the alignment to a 10-bit comma. The RX receiving unaligned bits are on the
1 00 10 11 0 00 01 00 1 00 110 10 11 10 0 11 00 11 10 0101 111 1001 011 0110 010 1010 010 0010 101 0101 0110 011 0
All Subsequent Data
Aligned to Correct
Byte Boundary
www.xilinx.com
for more information about use models.
Stream of Serial Data
Alignment Block
Finds Comma
7 Series FPGAs GTP Transceivers User Guide
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UG482 (v1.9) December 19, 2016