VSC8113
Data Sheet
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).
D
Q
D
Q
1:8
RXOUT[7:0]
TXIN[7:0]
CRU
RXDATAIN
Serial to
Parallel
Recovered
Clock
0
1
RXCLKIN
1
0
Q
D
Q
D
8:1
Parallel to
Serial
TXDATAOUT
1
0
TXCLKOUT
FACLOOP
PLL
Figure 3. Facility Loopback Data Path
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 parallel-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 at the low-speed parallel outputs (RXOUT[7:0]). See Figure 4 on page 6. The internally generated
155MHz/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 at the high-speed output (TXDATAOUT),
along with the high-speed transmit clock (TXCLKOUT) which is 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±.
5 of 22
G52154, Rev 4.5
6/28/02
Confidential
VITESSE [ VITESSE SEMICONDUCTOR CORPORATION ]
