VITESSE

SEMICONDUCTOR CORPORATION

®

Advance Product Information

VSC7182

Quad Transceiver

for Gigabit Ethernet and Fibre Channel

Page 4

G52307-0, Rev 2.2

10/10/00

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Tel: (800) VITESSE • FAX: (805) 987-5896 • Email: prodinfo@vitesse.com

Internet: www.vitesse.com

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

Corrupt

Corrupt

Corrupt

K28.5

Data1

Data2

Data3

K28.5

Data

RCi0

RCi1

RCi0

RCi1

SYNi

RXi[0:9]

([RCM HIGH)

(RCM LOW)

Misaligned Comma: Stretched

Aligned Comma