XRT73R12_07 Datasheet, PDF (45/89 Pages) Exar Corporation – TWELVE CHANNEL E3/DS3/STS-1 LINE INTERFACE UNIT

XRT73R12
REV. 1.0.2
TWELVE CHANNEL E3/DS3/STS-1 LINE INTERFACE UNIT
6.2 LOOPBACKS
The XRT73R12 offers three loopback modes for diagnostic purposes. The loopback modes are selected via
the RLB_n and LLB_n bits n the Channel control registers select the loopback modes.
6.2.1 ANALOG LOOPBACK
In this mode, the transmitter outputs TTIP_n and TRing_n are internally connected to the receiver inputs
RTIP_n and RRing_n as shown in Figure 30. Data and clock are output at RxClk_n, RxPOS_n and RxNEG_n
pins for the corresponding transceiver. Analog loopback exercises most of the functional blocks of the device.
NOTES:
1. In the Analog loopback mode, data is also output via TTIP_n and TRing_n pins.
2. Signals on the RTIP_n and RRing_n pins are ignored during analog loopback.
FIGURE 30. ANALOG LOOPBACK
TxClk
TxPOS
TxNEG
HDB3/B3ZS
ENCODER
TIMING
Tx
CONTROL
TTIP
TRing
RxClk
RxPOS
RxNEG
HDB3/B3ZS
DECODER
DATA &
CLOCK
Rx
RECOVERY
RTIP
RRing
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