XRT91L81IB View Datasheet(PDF) - Exar Corporation
Part Name
Description
MFG CO.
'XRT91L81IB' PDF : 40 Pages View PDF
XRT91L81
2.488/2.666GBPS OC-48/STM-16 SONET/SDH TRANSCEIVER
REV. P1.0.3
PRELIMINARY
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 along with the high-speed transmit clock which is generated from the clock
multiplier unit and presented to the TXO2P/N pins. A simplified block diagram of digital loopback is shown in
Figure 16.
FIGURE 16. DIGITAL LOOPBACK
Tx Parallel Input
Digital Loopback
FIFO
PISO
Re-Timer
Output Drivers
Tx Serial Output
Rx Parallel Output
SIPO
CDR
Input MUX
24
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