Altera Stratix GX Transceiver - Manual (Page 53)

Altera Corporation 3–7
January 2005 Stratix GX Transceiver User Guide
Basic Mode
The byte boundary is locked after the first comma is detected and aligned
after the rising edge of the rx_enacdet[] signal. If the byte boundary
changes, the rx_enacdet[] signal must be deasserted and reasserted
to reset the alignment circuit. On the rising edge of the rx_enacdet[],
the word aligner locks onto the first comma detected. In this scenario, the
rx_patterndetect[]
signal is asserted to signify that the comma has
been aligned. Also, the rx_syncstatus[] signal is asserted for a clock
cycle to signify that the word boundary has been synchronized. After the
word boundary has been locked, regardless of whether the
rx_enacdet[]
is high or low, the rx_syncstatus[] signal asserts
itself for one clock cycle whenever a comma is detected across a different
byte boundary. The rx_syncstatus[] signal operates in this re-
synchronization state until a rising edge is detected on rx_enacdet[].
Figure 3–6 shows how the word aligner signals interact in 16-bit
alignment mode for an A1A2 pattern.
Figure 3–6. Example of How the Word Aligner Signals Interact in SONET A1A2 Manual Alignment Mode
In Figure 3–6 , the rx_enacdet signal is toggled high at time n, at which
point the aligner locks to the boundary of the next present comma. The
A1 comma also appears on the rx_word_align_out port during this
period. At time n+1 the A2 comma appears on the rx_word_align_out
port. Because the comma exists, the rx_patterndetect and
rx_syncstatus
signals are asserted for one clock cycle to signify that
the A1A2 comma has been detected and the word boundary has been
locked. The A1A2 comma appears again across word boundaries during
periods n+2, n+3, and n+4. The rx_enacdet signal is held high, but the
word aligner does not re-align the byte boundary as it would in 10-bit
manual alignment mode. Instead, the rx_syncstatus signal is asserted
for one clock cycle to signify a re-synchronization condition. You must
deassert and reassert the rx_enacdet signal to retrigger the word
aligner. The next transition occurs at time n+5, where rx_enacdet is
rx_recovclockout
rx_enacdet
rx_patterndetect
rx_syncstatus
rx_word_align_out
01101111 00010100 111110000 01101111 00000001 00010100
n n+1 n+2 n+3 n+4 n+5 n+6
01000110