®
VITESSE
SEMICONDUCTOR CORPORATION
Quad Transceiver
for Gigabit Ethernet and Fibre Channel
Advance Product Information
VSC7182
Word Alignment
The VSC7182 provides 7-bit comma character recognition and data word alignment. Word synchronization
is enabled on all channels by asserting SYNC HIGH. When synchronization is enabled, the receiver examines
the recovered serial data for the presence of the “Comma” pattern. This pattern is “0011111XXX”, where the
leading zero corresponds to the first bit received. The comma sequence is not contained in any normal 8B/10B
coded data character or pair of adjacent characters. It occurs only within special characters, known as K28.1,
K28.5 and K28.7, which are defined for synchronization purposes. Improper comma alignment is defined as
any of the following conditions:
1) The comma is not aligned within the 10-bit transmission character such that RXi(0...6) = “0011111.”
2) The comma straddles the boundary between two 10-bit transmission characters.
3) The comma is properly aligned but occurs in the received character presented during the rising edge of
RCi0 rather than RCi1.
When SYNC is HIGH and an improperly aligned comma is encountered, the recovered clock is stretched,
never slivered, so that the comma character and recovered clocks are aligned properly to RXi[0:9]. This results
in proper character and word alignment. When the parallel data alignment changes in response to a improperly
aligned comma pattern, data which would have been presented on the parallel output port prior to the comma
character, and possibly the comma character itself, may be lost. Possible loss of the comma character is data
dependent, according to the relative change in alignment. Data subsequent to the comma character will always
be output correctly and properly aligned. When SYNC is LOW, the current alignment of the serial data is main-
tained indefinitely, regardless of data pattern.
On encountering a comma character, SYNi is driven HIGH. The SYNi pulse is presented simultaneously
with the comma character and has a duration equal to the data. The SYNi signal is timed such that it can be cap-
tured by the adjoining protocol logic on the rising edge of RCi1. Functional waveforms for synchronization are
given in Figure 2. The first K28.5 shows the case where the comma is detected, but it is misaligned so a change
in the output data alignment is required. Note that up to three characters prior to the comma character may be
corrupted by the realignment process. The second K28.5 shows the case when a comma is detected and no
phase adjustment is necessary. It illustrates the position of the SYNi pulse in relation to the comma character on
RXi[0:9].
Figure 2: Misaligned and Aligned K28.5 Characters
RCi0
(RCM LOW)
RCi1
RCi0
([RCM HIGH)
RCi1
SYNi
RXi[0:9]
Data
Corrupt Corrupt Corrupt
Misaligned Comma: Stretched
K28.5
Data1
Data2
Data3
K28.5
Aligned Comma
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VITESSE
SEMICONDUCTOR CORPORATION
• 741 Calle Plano • Camarillo, CA 93012
Tel: (800) VITESSE • FAX: (805) 987-5896 • Email: prodinfo@vitesse.com
Internet: www.vitesse.com
G52307-0, Rev 2.2
10/10/00
VITESSE [ VITESSE SEMICONDUCTOR CORPORATION ]
