VITESSE

SEMICONDUCTOR CORPORATION

Data Sheet

VSC8113

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

with Integrated Clock Generation and Clock Recovery

Page 6

© VITESSE SEMICONDUCTOR CORPORATION

G52154-0, Rev 4.2

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

3/19/99

Split Loopback

Equipment and facility loopback modes can be enabled simultaneously. In this case, high-speed serial data

received (RXDATAIN) and received/recovered clock are mux’d through to the high-speed serial outputs

(TXDATAOUT) and (TXCLKOUT). The low-speed transmit byte wide bus(TXIN[7:0]) and (TXLSCKIN) are

mux’d into the low-speed byte wide receive output bus (RXOUT[7:0]) and (RXLSCKOUT). See Figure 5.

Figure 5: Split Loopback Datapath

Loop Timing

LOOPTIM0 mode bypasses the CMU when the LOOPTIM0 input is asserted high. In this mode the CMU

is bypassed by using the receive clock (RXCLKIN), and the entire part is synchronously clocked from a single

external source.

LOOPTIM1 mode bypasses the REFCLK input and uses the divide-by-8 version of the receive clock as the

reference input to the CMU. This mode is selected by asserting the LOOPTIM1 input high. The part is forced

out of this mode if it is in the Loss of Signal state or in Equipment Loopback to prevent the CMU from feeding

its own clock back.

Clock Synthesis

The VSC8113 uses an integrated phase-locked loop (PLL) for clock synthesis of the 622MHz high speed

clock used for serialization in the transmitter section. The PLL is comprised of a phase-frequency detector

(PFD), an integrating operation amplifier and a voltage controlled oscillator (VCO) configured in classic feed-

back system. The PFD compares the selected divided down version of the 622MHz VCO (select pins B0-B2

select divide-by ratios of 8, 12, 16 and 32, see Table 12) and the reference clock. The integrator provides a trans-

fer function between input phase error and output voltage control. The VCO portion of the PLL is a voltage con-

trolled ring-oscillator with a center frequency of 622MHz.

The reactive elements of the integrator are located off-chip and are connected to the feedback loop of the

amplifier through the CP1, CP2, CN1 and CN2 pins. The configuration of these external surface mounted

capacitors is shown in Figure 6. Table 1 shows the recommended external capacitor values for the configurable

reference frequencies.

D

Q

D

Q

1:8

Serial to

Parallel

Q

D

RXDATAIN

TXDATAOUT

RXOUT[7:0]

Q

D

8:1

Parallel to

Serial

TXIN[[7:0]

0

1

CRU

RXCLKIN

TXCLKOUT

TXLSCKIN

RXLSCKOUT

DSBLCRU

Recovered

Clock