XRT75R12D_06 Datasheet, PDF (47/134 Pages) Exar Corporation – TWELVE CHANNEL E3/DS3/STS-1 LINE INTERFACE UNIT WITH SONET

XRT75R12D
REV. 1.0.1 TWELVE CHANNEL E3/DS3/STS-1 LINE INTERFACE UNIT WITH SONET DESYNCHRONIZER
6.2 LOOPBACKS
The XRT75R12D 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
including the jitter attenuator which can be selected in either the transmit or receive path.
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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