2–76
Altera Corporation
Stratix II GX Device Handbook, Volume 2
October 2007
Receiver Modules
Manual 10-Bit Alignment Mode
You can configure the word aligner to align to a 10-bit word boundary.
The internal word alignment circuitry shifts to the correct word boundary
if the alignment pattern specified in the pattern detector is detected in the
data stream.
The
rx_enapatternalign
port enables the word alignment in the
manual 10-bit alignment mode. When the
rx_enapatternalign
signal
is high, the word aligner detects the specified alignment pattern and
realigns the byte boundary if necessary. The
rx_syncstatus
port is
asserted for one parallel clock cycle to signify that the word boundary has
been detected across the word boundary and has synchronized to the
new boundary.
The
rx_enapatternalign
signal is held high if the alignment pattern
is known to be unique and does not appear across the byte boundaries of
other data. For example, if an 8B/10B encoding scheme guarantees that
the /K28.5/ code group is a unique pattern in the data stream, the
rx_enapatternalign
port is held at a constant high.
If the alignment pattern can exist between word boundaries, the
rx_enapatternalign
port must be controlled by the user logic in the
PLD to avoid false word alignment. For example, assume that 8B/10B is
used and a /+D19.1/ (b'110010 1001) character is specified as the
alignment pattern. In this case, a false word boundary is detected if a
/-D15.1/ (b'010111 1001) is followed by a /+D18.1/ (b'010011 1001). Refer
to
Figure 2–60
.
Figure 2–60. False Word Boundary Alignment if Alignment Pattern Exists Across Word Boundaries, Single
Width
In this example, the
rx_enapatternalign
signal is deasserted after the
word aligner locates the initial word alignment to prevent false word
boundary alignment. When the
rx_enapatternalign
signal is
deasserted, the current word boundary is locked even if the alignment
pattern is detected across different boundaries. In this case, the
rx_syncstatus
acts as a re-synchronization signal to signify that the
…..
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0
1
0
1
1
1
1
0
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1
0
1
0
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1
0
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-
D15.1
+D18.1
+D19.1