VITESSE

SEMICONDUCTOR CORPORATION

Preliminary Datasheet

VSC7139

Quad Transceiver for

Gigabit Ethernet and Fibre Channel

Page 4

G52196-0, Rev 3.3

5/14/01

© VITESSE SEMICONDUCTOR CORPORATION • 741 Calle Plano • Camarillo, CA 93012

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

Internet: www.vitesse.com

Word Alignment

The VSC7139 provides 7-bit comma character recognition and data word alignment. Word synchronization

is enabled on all channels by asserting ENCDET HIGH. When synchronization is enabled, the receiver exam-

ines 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 Rx(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

RCx0 rather than RCx1.

When ENCDET 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 Rx(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 charac-

ter 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 ENCDET is LOW, the current alignment of the

serial data is maintained indefinitely, regardless of data pattern.

On encountering a comma character, SYNCx is driven HIGH. The SYNCx pulse is presented simulta-

neously with the comma character and has a duration equal to the data. The SYNCx signal is timed such that it

can be captured by the adjoining protocol logic on the rising edge of RCx1. Functional waveforms for synchro-

nization 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 charac-

ter 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. Figure 2 illustrates the position of the SYNCx pulse in relation to the

comma character on Rx(0:9).

Figure 2: Misaligned and Aligned K28.5 Characters

Corrupt

Corrupt

Corrupt

K28.5

Data1

Data2

Data3

K28.5

Data

RCx0

RCx1

RCx0

RCx1

SYNCx

Rx(0:9)

(RCM HIGH)

(RCM LOW)

Misaligned Comma: Stretched

Aligned Comma