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).
RXDATAIN
CRU
D
Q
1:8
Serial to
Parallel
D
Q
RXOUT[7:0]
Recovered
Clock
0
1
Q
D
RXCLKIN
TXDATAOUT
1
0
8:1
Parallel to
Serial
Q
D
TXIN[7:0]
TXCLKOUT
1
0
PLL
FACLOOP
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) that is generated by the on-chip clock multiplier unit.
CRU Equipment Loopback
The CRU Equipment Loopback function is the same as Equipment Loopback; the point at 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 4.7
5/16/03
VITESSE [ VITESSE SEMICONDUCTOR CORPORATION ]
