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XRT83SL28
REV. 1.0.0
8-CHANNEL E1 SHORT-HAUL LINE INTERFACE UNIT
3.1.3
Digital Loopback
With digital loopback activated, the transmit input data at TCLK/TPOS/TNEG is looped back to the receive
output data at RCLK/RPOS/RNEG. The receive input data at RTIP/RRING is ignored while valid transmit
output data continues to be sent to the line. A simplified block diagram of digital loopback is shown in
Figure 20.
FIGURE 20. SIMPLIFIED BLOCK DIAGRAM OF DIGITAL LOOPBACK
TAOS
TCLK
TPOS
TNEG
Timing
Control
TTIP
TRING
Encoder
Decoder
JA
JA
Tx
RCLK
RPOS
RNEG
Data and
Clock
Recovery
RTIP
RRING
Rx
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