Altera Stratix GX Transceiver - Manual (Page 51)

Altera Corporation 3–5
January 2005 Stratix GX Transceiver User Guide
Basic Mode
Manual Alignment Modes
The Stratix GX device supports manual alignment in 10-bit, 16-bit, and
bit-slipping modes.
Manual 10-Bit Alignment Mode
You can configure the word aligner to align to a 10-bit word boundary if
you use 8B/10B encoding or if you specify the data width to be either 10-
or 20-bits wide. In this mode, the internal word alignment circuitry barrel
shifts the correct word boundary if the comma specified in the pattern
detector is detected in the data stream.
When rx_enacdet[] is high, the word aligner detects the specified
comma and re-aligns the byte boundary, if needed. The
rx_syncstatus[]
signal is asserted for one clock cycle to signify that
the word boundary has been synchronized. The rx_enacdet[] signal
can be held high if the comma is known to be unique and does not also
appear across the byte boundaries of other data. For example, if the
design uses an encoding scheme such as 8B/10B to guarantee that the
/K28.5/ code group is a unique pattern in the data stream, the
rx_enacdet
is held high. In situations where the comma exists between
word boundaries, rx_enacdet must be controlled to avoid false word
alignment. For example, suppose that you use 8B/10B encoding and
specify a /+D19.1/ (b'110010 1001) character as the comma. 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). (See
Figure 3–4 .)
Figure 3–4. False Word Boundary Alignment if the Comma Exists Across Word Boundaries
The rx_enacdet signal must be deasserted after the initial word
alignment is found, so as to prevent false word boundary alignment.
When rx_enacdet is deasserted, the current word boundary is locked
even if the comma is detected across different boundaries. In this case,
rx_syncstatus[]
acts as a re-synchronization signal to signify that the
comma was detected, but the boundary is different than the current
boundary. For best results, monitor this signal and reassert
rx_enacdet[]
, if re-alignment is desired.
….. ..
0 1 0 1 1 1 1 0 0 1 0 1 0 0 0 1
-D15.1 +D18.1
+D19.1
….. ..
0 1 1 1