VITESSE

SEMICONDUCTOR CORPORATION

Data Sheet

VSC8117

ATM/SONET/SDH 622/155 Mb/s Transceiver Mux/Demux

with Integrated Clock Generation and Clock Recovery

Page 4

© VITESSE SEMICONDUCTOR CORPORATION

G52221-0, Rev 4.1

741 Calle Plano, Camarillo, CA 93012 • 805/388-3700 • FAX: 805/987-5896

1/8/00

Loss of Signal

The VSC8117 features Loss of Signal (LOS) detection. Loss of Signal is declared if the incoming serial

data stream has no transition continuously for more than 128 bits. During an LOS condition, the VSC8117

forces the receive data low which is an indication for any downstream equipment that an optical interface failure

has occurred. The receive section continues to be clocked by the CRU as it is now locked to the CRUREFCLK

unless DSBLCRU is active or CRUREFSEL is inactive in which case it will be clocked by the CMU. This LOS

condition will be removed when the part detects more than 16 transitions in a 128 bit time window. This LOS

detection feature can be disabled by applying a high level to the LOSDETEN_ input. The VSC8117 also has a

PECL input LOSPECL to force the part into a Loss of Signal state. Most optics have a PECL output usually

called “SD” or “FLAG” indicating a lack of or presence of optical power. Depending on the optics manufacturer

this signal is either active high or active low. The LOSPECL input on the VSC8117 is active low.

Figure 2: Data and Clock Receive Block Diagram

Facility Loopback

The Facility Loopback function is controlled by the FACLOOP signal. When the FACLOOP signal is set

high, the Facility Loopback mode is activated and the high speed serial receive data (RXDATAIN) is presented

to the high speed transmit output (TXDATAOUT). See Figure 3. In Facility Loopback mode the high speed

receive data (RXDATAIN) is also converted to parallel data and presented to the low speed receive data output

pins (RXOUT[7:0]). The receive clock (RXCLKIN) or the recovered clock is also divided down and presented

to the low speed clock output (RXLSCKOUT).

DQ

DQ

DQ

0

1

Divide-by-8

CMU

DQ

PM5355

DQ

RXOUT[7:0]

FP

RXLSCKOUT

VSC8117

CRU

RXDATAIN+/-

RXCLKIN+/-

DSBLCRU

0

1

0

1

LOSPECL

LOSDETEN_