VSC7216-02
Data Sheet
word alignment, a synchronization point must be seen across all aligned receive channels within the allotted 12 or 40
bit time window. The VSC7216-02 receiver recognizes the first four characters of the Word Sync Sequence (either
K28.5+ K28.5+ K28.5– K28.5– or K28.5– K28.5– K28.5+ K28.5+) as the synchronization point. As a model for
understanding, consider the case where a VSC7216-02 transmitter sends 32 bits of data to the receiver through copper
media, which has small cable length differences causing a channel-to-channel skew. All transmit channels that are to
be word aligned transmit the Word Sync Sequence in parallel. On detection of the synchronization point, the receivers
will reposition the recovered data within their elastic buffers in order to align all channels and remove any
channel-to-channel skew. All normal data characters following the Word Sync Sequence will be properly word
aligned. In the process of channel alignment, one or two of the final twelve K28.5 characters in the Word Sync
Sequence may be deleted or duplicated. This ensures that each transmitted 32-bit word is recovered correctly.
The VSC7216-02 is capable of performing rate matching in word-aligned applications by inserting or deleting IDLEs
in parallel across the aligned receive channels. This requires that the word-aligned data streams contain IDLEs
inserted in parallel on all transmit channels (i.e., an IDLE “word”) according to the IDLE density requirement
previously described.
Word alignment is enabled by connecting the WSI input to a WSO output, either from the same device if a single
device is used, or from another device if multiple devices are used in parallel to align more than four channels. The
FLOCK input state and WSI input source determine whether or not rate matching (IDLE deletion or duplication) will
be performed, and whether it is done independently on each channel or in parallel across aligned channels. Word
alignment is disabled when WSI is not connected to a WSO output. Rate matching is disabled when either FLOCK is
HIGH or WSI is held LOW (see Table 8).
Table 8. Word Alignment and Rate Matching Control
FLOCK
WSI Source
Word Alignment
Rate Matching
0
0
0
1
1
1
0
1
Off
Off
Off
Enabled, Independent Channels
WSO
0
Enabled
Off
Enabled, Aligned Channels
Off
Off
Off
1
Off
WSO
Enabled
There are four distinct modes of operation defined in Table 8. The first row disables both word alignment and rate
matching. (The fourth and fifth row configurations function identically to the first row.) The second row configures
the channels to operate independently with rate matching. Word alignment is disabled, and IDLEs will be dropped/
duplicated independently in each channel as required. The third row configures the part to perform word alignment
and rate matching. The receive channels will be aligned per the device driving WSO, and IDLE words will be
dropped/duplicated across the aligned channels as required. The last row configures the part to perform word
alignment and disables rate matching. This mode of operation is appropriate for a frequency-locked application where
it is desired to align the receive channels without altering the received data streams.
Using Multiple VSC7216-02s in Parallel
Multiple VSC7216-02s can be used in parallel to form wider bus widths. In order for word alignment to function
correctly across multiple devices, each transmit channel’s input data must be transmitted on a common clock, and
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G52367 Revision 4.2
December 2006
VITESSE [ VITESSE SEMICONDUCTOR CORPORATION ]
