VITESSE

SEMICONDUCTOR CORPORATION

Data Sheet

VSC8113

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

with Integrated Clock Generation and Clock Recovery

Page 4

© VITESSE SEMICONDUCTOR CORPORATION

G52154-0, Rev 4.2

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

3/19/99

Loss of Signal

The VSC8113 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 VSC8113

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 “CRUREF-

CLK” unless “DSBLCRU” is active 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 LOSDETEN_ input. The VSC8113 also has a TTL input LOSTTL

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

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

factured this signal is either active high or active low. The LOSTTL and LOSPECL inputs are XNOR’d to

generate an internal LOS control signal. See Figure 2. The optics “SD” output should be connected to

LOSPECL. The LOSTTL input should be tied low if the optics “SD” output is active high. If it’s active low tie

LOSTTL high. The inverse is true if the optics use “FLAG” for loss of signal.

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

at the high speed transmit output (TXDATAOUT). See Figure 3. In addition, the high speed received/recovered

clock is selected and presented at the high speed transmit clock output (TXCLKOUT). In Facility Loopback

mode the high speed receive data (RXDATAIN) is also converted to parallel data and presented at the low speed

receive data output pins (RXOUT[7:0]). The receive clock (RXCLKIN) is also divided down and presented at

the low speed clock output (RXLSCKOUT).

DQ

DQ

DQ

0

1

Divide-by-8

CMU

DQ

PM5355

DQ

RXOUT[7:0]

FP

RXLSCKOUT

VSC8113

CRU

RXDATAIN+/-

RXCLKIN+/-

DSBLCRU

0

1

0

1

CRULOCKDET

LOSTTL

LOSPECL

LOSDETEN_