XRT91L80 View Datasheet(PDF) - Exar Corporation
Part Name
Description
MFG CO.
'XRT91L80' PDF : 45 Pages View PDF
xr
REV. P1.1.0
PRELIMINARY
XRT91L80
2.488/2.666 GBPS STS-48/STM-16 SONET/SDH TRANSCEIVER
4.3 Digital Local Loopback
The digital local loopback is activated when the DLOOP signal is set "High." When digital local loopback is
activated, the high-speed data from the output of the parallel to serial converter is looped back and presented
to the high-speed input of the receiver serial to parallel converter. The CMU output is also looped back to the
receive section and is used to synchronize the transfer of the data through the receiver. In Digital loopback
mode, the transmit data from the transmit parallel interface TXDI[3:0]P/N is serialized and presented to the
high-speed transmit output TXOP/N using the high-speed 2.488/2.666 GHz transmit clock which is generated
from the clock multiplier unit and presented to the input of the Retimer and SIPO. A simplified block diagram of
digital loopback is shown in Figure 18.
FIGURE 18. DIGITAL LOOPBACK
TX Parallel Input
Digital Loopback
FIFO
PISO
Re-Timer
CML
Output Drivers
TX Serial Output
RX Parallel Output
SIPO
CDR
CML
Input Drivers
25
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