XRT73R12_07 Datasheet, PDF (46/89 Pages) Exar Corporation – TWELVE CHANNEL E3/DS3/STS-1 LINE INTERFACE UNIT

XRT73R12
TWELVE CHANNEL E3/DS3/STS-1 LINE INTERFACE UNIT
REV. 1.0.2
6.2.2 DIGITAL LOOPBACK
When the Digital Loopback is selected, the transmit clock TxClk_n and transmit data inputs (TxPOS_n &
TxNEG_n are looped back and output onto the RxClk_n, RxPOS_n and RxNEG_n pins as shown in
Figure 31.
FIGURE 31. DIGITAL LOOPBACK
TxCLK
TxPOS
TxNEG
HDB3/B3ZS
ENCODER
TIMING
Tx
CONTROL
TTIP
TRing
RxCLK
RxPOS
RxNEG
HDB3/B3ZS
DECODER
DATA &
CLOCK
Rx
RECOVERY
RTIP
RRing
6.2.3 REMOTE LOOPBACK
With Remote loopback activated as shown in Figure 32, the receive data on RTIP and RRing is looped back
after the Data and Clock Recovery to the transmit path using RxClk as transmit timing. The receive data is
also output via the RxPOS and RxNEG pins.
NOTE: Input signals on TxClk, TxPOS and TxNEG are ignored during Remote loopback.
FIGURE 32. REMOTE LOOPBACK
TxCLK
TxPOS
TxNEG
HDB3/B3ZS
ENCODER
TIMING
CONTROL
Tx
TTIP
TRing
RxCLK
RxPOS
RxNEG
HDB3/B3ZS
DECODER
DATA &
CLOCK
RECOVERY
RTIP
Rx
RRing
43