Altera Stratix GX Transceiver - Manual (Page 118)

5–6 Altera Corporation
Stratix GX Transceiver User Guide January 2005
XAUI Mode Receiver Architecture
Word Aligner
For embedded clocking schemes, the clock is recovered from the
incoming data stream based on the transition density of the data. This
feature eliminates the need for you to factor in receiver skew margins
between the clock and data. However, with this clocking methodology,
the word boundary of the re-timed data can be altered. Stratix GX
transceivers offer an embedded word alignment circuit that can be used
in conjunction with the pattern detector to align the word boundary of the
re-timed data to a specified comma. You can configure this embedded
circuit to synchronize with the XAUI protocols.
The word aligner is composed of a pattern detector and synchronization
state machines. The word aligner cannot be bypassed, but if the
rx_enacdet
signal is not used, the word aligner does not alter the data.
Figure 5–5 shows the various components of the word aligner. The
functionality of each component is described in the following sections.
Figure 5–5. Stratix GX Word Aligner Components
Pattern Detector Module
The pattern detector matches a pre-defined comma to the current byte
boundary. If the comma is found, the optional rx_patterndetect
signal is asserted for the duration of one clock cycle to signify that the
comma exists in the current word boundary. The pattern detector module
indicates only that the signal exists and does not modify the word
boundary. Modification of the word boundary is discussed in the word
alignment and synchronization sections. You can program a 10-bit
pattern for the pattern detector to recognize.
WORD ALIGNER
PATTERN
DETECTOR
SYNCHRONIZATION
STATE MACHINES
10-BIT
MODE XAUI
MODE