CertusPro-NX SerDes/PCS Usage Guide
Preliminary
Technical Note
FPGA-TN-02245-0.81
© 2020-2021 Lattice Semiconductor
57
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Word Aligner
The word boundary of the upstream transmitter is lost upon deserialization, considering that the data is serialized
before transmission and then de-serialized at the receiver. The word aligner receives parallel data from the
De-Serializer and restores the word boundary.
To make alignment possible, transmitters send a recognizable sequence (usually a COMMA) periodically. The receiver
searches for the COMMA in the incoming data. Once the receiver finds the COMMA, it moves the COMMA to a byte
boundary, and the received parallel words match the transmitted parallel words.
is the block diagram of the Word Aligner module.
Auto Aligner
Manual
Aligner
Link
Sync
FSM
8B/10B
decoder
get_lsync
walign_en
walign_en
10-bit code
aligned_data
parallel data
8-bit code
code error
Word Aligner
Figure 6.11. Word Aligner Block Diagram
The Word Aligner module supports automatic alignment mode. This module search for word alignment pattern in the
input parallel data, then move the matched pattern to byte boundary and align the output data to the boundary. The
alignment operation is performed when walign_en signal is high. Otherwise, the module will lock the current boundary
and avoid re-alignment. The walign_en signal can be driven either by user logic or by Link Synchronization FSM which is
a state machine to detect the loss of link synchronization and signal the re-alignment request.
To support applications which need deterministic and lower latency, CertusPro-NX SerDes/PCS also supports manual
alignment mode (or bit slip mode in some documents). In manual mode, fabric can drive the skipbit signal high to
control the input parallel data shifting inside PMA. User logic can count how many cycles the skipbit signal is high so as
to know the total number of shifted bits inside PMA.
The link synchronization is an extension of the word aligner. The state machine implements hysteresis during link
synchronization. The number of synchronization code groups that the link must receive to acquire synchronization and
the number of erroneous code groups that it must receive to fall out of synchronization are programmable.
is the Link Synchronization FSM.