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XRT91L30 View Datasheet(PDF) - Exar Corporation

Part NameDescriptionManufacturer
XRT91L30 STS-12/STM-4 OR STS-3/STM-1 SONET/SDH TRANSCEIVER Exar
Exar Corporation Exar
XRT91L30 Datasheet PDF : 39 Pages
First Prev 31 32 33 34 35 36 37 38 39
xr
REV. 1.0.1
XRT91L30
STS-12/STM-4 OR STS-3/STM-1 SONET/SDH TRANSCEIVER
4.3 Analog Local Loopback
Analog Local Loopback (ALOOP) controls a more comprehensive version of digital local loopback in which the
point where the transmit data is looped back is moved all the way back to the high-speed receive I/O. The
transmit data from the transmit parallel interface TXDI[7:0] is serialized and presented to the high-speed
transmit output TXOP/N using the high-speed 622.08/155.52 MHz transmit clock generated from the clock
multiplier unit. In addition, the high-speed transmit data TXOP/N is looped back to the receive clock and data
recovery unit, replacing the RXIP/N. The signal is then processed by the CDR, and is sent through the serial to
parallel converter and presented at the low-speed receive parallel interface RXDO[7:0]. ALOOP is invoked by
asserting the ALOOP pin "High." A simplified block diagram of parallel remote loopback is shown in Figure 20.
Receive Data mute upon LOS, as shown in Figure 7, applies to Analog Local Loopback.
FIGURE 20. ANALOG LOCAL LOOPBACK
Tx Parallel Input
Rx Parallel Output
Analog Local Loop back
PISO
Re-Timer
SIPO
CDR
LVPECL
Input Drivers
LVPECL
Output Drivers
Tx Serial Output
4.4 Split Loopback
The serial remote loopback and the digital local loopback can be combined to form a split loopback. 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 high-speed serial receive data from RXIP/N is presented at the high speed
transmit output TXOP/N, and the high-speed recovered clock is selected to re-time the high speed transmit
data output. A simplified block diagram of parallel remote loopback is shown in Figure 21.
FIGURE 21. SPLIT LOOPBACK
Tx Parallel Input
Rx Parallel Output
Split Loopback
PISO
SIPO
Re-Timer
LVPECL
Output Drivers
Tx Serial Output
CDR
LVPECL
Input Drivers
Rx Serial Input
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