XRT75L03D Datasheet, PDF (92/134 Pages) Exar Corporation – THREE CHANNEL E3/DS3/STS-1 LINE INTERFACE UNIT WITH SONET DESYNCHRONIZER

XRT75L03D
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REV. 1.0.0 THREE CHANNEL E3/DS3/STS-1 LINE INTERFACE UNIT WITH SONET DESYNCHRONIZER
8.2.2 DIGITAL LOOPBACK:
The Digital Loopback function is available either in Hardware mode or Host mode. When the Digital Loopback
is selected, the transmit clock (TxClk_n) and transmit data inputs (TPDATA_n & TNDATA_n) are looped back
and output onto the RxClk_n, RPOS_n and RNEG_n pins as shown in Figure 27.
FIGURE 27. DIGITAL LOOPBACK
TCLK
TPDATA
TNDATA
1
HDB3/B3ZS
ENCODER
TIMING
Tx
CONTROL
TTIP
TRING
RCLK
RPOS
RNEG
1
HDB3/B3ZS
DECODER
1 _{if enabled}
2 _{if enabled and selected in either Receive or}
Transmit path
DATA &
CLOCK
Rx
RECOVERY
RTIP
RRING
8.2.3 REMOTE LOOPBACK:
With Remote loopback activated as shown in Figure 28, the receive data on RTIP and RRING is looped back
after the jitter attenuator (if selected in receive or transmit path) to the transmit path using RxClk as transmit
timing. The receive data is also output via the RPOS and RNEG pins.
During the remote loopback mode, if the jitter attenuator is selected in the transmit path, the receive data after
the Clock and Data Recovery Block is looped back to the transmit path and passed through the jitter attenuator
using RxClk as the transmit timing.
NOTE: Input signals on TxClk, TPDATA and TNDATA are ignored during Remote loopback.
FIGURE 28. REMOTE LOOPBACK
TCLK
TPDATA
TNDATA
1
HDB3/B3ZS
ENCODER
TIMING
CONTROL
Tx
TTIP
TRING
RCLK
RPOS
RNEG
1
HDB3/B3ZS
DECODER
1 _{if enabled}
2 _{if enabled and selected in either Receive or}
Transmit path
DATA &
CLOCK
RECOVERY
RTIP
Rx
RRING
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