Altera Corporation
2–91
October 2007
Stratix II GX Device Handbook, Volume 2
Stratix II GX Transceiver Architecture Overview
In 20-bit manual word alignment mode, the word aligner looks for the
20-bit alignment pattern after detecting a rising edge on the
rx_enapatternalign
signal. On finding the alignment pattern, the
word aligner locks the word boundary and asserts the
rx_syncstatus
signal. The
rx_syncstatus
signal remains high until it sees another
rising edge on the
rx_enapatternalign
. After detecting a rising edge
on the
rx_enapatternalign
signal, the word aligner starts looking for
the 20-bit word alignment pattern again and asserts the
rx_syncstatus
signal once it finds the 20-bit alignment pattern. The
rx_enapatternalign
port can only operate in an edge-sensitive
fashion in double-width mode. Deassertion of the
rx_enapatternalign
port is necessary for realignment. Altera
recommends that you include the /K28.5/ code group as one of the
control codes in this alignment pattern.
Manual 32-Bit Alignment Mode
You can enable the 32-bit alignment mode in the double-width mode
only. This mode aligns to the 32-bit alignment pattern you specified in the
MegaWizard.
The byte boundary is locked after the first alignment pattern is detected
and then after the rising edge of the
rx_enapatternalign
port. If the
byte boundary changes, the
rx_enapatternalign
port must be
deasserted and reasserted to enable the alignment circuit to search for and
align to the next available alignment pattern. On the rising edge of
rx_enapatternalign
, the word aligner locks onto the first alignment
pattern detected. In this scenario, the
rx_patterndetect
is asserted to
signify that the alignment pattern has been aligned. The
rx_syncstatus
signal is asserted to signify that the word boundary has
been synchronized.
Manual Bit-Slipping Alignment Mode
In the double-width mode, word alignment is also achieved by enabling
the manual bit-slip option in the MegaWizard. This mode operates the
same way as the bit slip in the single-width mode. With this option
enabled, the transceiver shifts the word boundary one bit from the MSB
to the LSB every parallel clock cycle. This occurs every time the
bit-slipping circuitry detects a rising edge of the
rx_bitslip
signal. At
each rising edge of
rx_bitslip
, the word boundary slips one bit. The
bit that arrives at the receiver first is skipped. When the word boundary
matches what you specified as the alignment pattern in the MegaWizard,
the
rx_patterndetect
signal is asserted for one clock cycle. You must
implement the logic in the PLD logic array to control the bit-slip circuitry.
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