VITESSE
SEMICONDUCTOR CORPORATION
Data Sheet
VSC8114
ATM/SONET/SDH 622 Mb/s Transceiver Mux/Demux
with Integrated Clock Generation and Clock Recovery
Equipment Loopback
The Equipment Loopback function is controlled by the EQULOOP signal. When the EQULOOP signal is
set high, the Equipment Loopback mode is activated and the high speed transmit data generated from the paral-
lel to serial conversion of the low speed data (TXIN[7:0]) is selected and converted back to parallel data in the
receiver section and presented to the low speed parallel outputs (RXOUT[7:0]). See Figure 4. The internally
generated 622MHz clock is used to generate the low speed receive clock output (RXLSCKOUT). In Equipment
Loopback mode the transmit data (TXIN[7:0]) is serialized and presented to the high speed output
(TXDATAOUT) using the clock generated by the on-chip clock multiplier unit.
CRU Equipment Loopback
Exactly the same as equipment loopback, the point where the transmit data is looped back is moved all the
way back to the high speed I/O. When the CRUEQLP signal is set high, transmit data is looped back to the
CRU, replacing RXDATAIN±
Figure 4: Equipment Loopback Data Path
D Q
D
Q
RXDATAIN
EQULOOP
0
1
1:8
Serial to
Parallel
RXOUT[7:0]
÷
8
Q
D
8:1
Parallel to
Serial
Q
D
RXLSCKOUT
TXIN[7:0]
TXLSCKIN
÷
8
TXLSCKOUT
TXDATAOUT
PLL
Split Loopback
Equipment and facility loopback modes can be enabled simultaneously. In this case, high-speed serial data
received (RXDATAIN) is mux’d through to the high-speed serial outputs (TXDATAOUT). The low-speed trans-
mit byte-wide bus (TXIN[7:0]) and (TXLSCKIN) is mux’d into the low-speed byte-wide receive output bus
(RXOUT[7:0]) and (RXLSCKOUT). See Figure 5.
Figure 5: Split Loopback Datapath
RXDATAIN
Recovered
Clock
CRU
D
Q
1:8
Serial to
Parallel
D
Q
RXOUT[7:0]
0
1
Q
D
8:1
Parallel to
Serial
Q
D
RXLSCKOUT
TXIN[[7:0]
RXCLKIN
DSBLCRU
TXDATAOUT
TXLSCKIN
G52185-0, Rev 4.0
11/1/99
©
VITESSE
SEMICONDUCTOR CORPORATION
741 Calle Plano, Camarillo, CA 93012 • 805/388-3700 • FAX: 805/987-5896
Page 5
VITESSE [ VITESSE SEMICONDUCTOR CORPORATION ]
