Datasheet

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Remote Loopback
PRBS
Power-On Reset
SLK2721
SLLS532B – JUNE 2002 – REVISED MARCH 2007
The RLOOP signal pin controls the remote loopback. When RLOOP is high, the serial receive data is selected
and presented on the serial transmit data output pins. The serial received data is also demultiplexed and
presented on the parallel receive data pins. The remote loop can be enabled only when the device is under
transceiver mode. When the device is put under the repeater mode with RX_MONITOR high, it performs the
same function as remote loopback.
Figure 4. Remote Loopback Data Path/Repeater Mode Operation
The SLK2721 device has two built-in pseudorandom bit stream (PRBS) functions. The PRBS generator is used
to transmit a PRBS signal. The PRBS verifier is used to check and verify a received PRBS signal.
When the PRBSEN pin is high, the PRBS generator and verifier are both enabled. A PRBS is generated and fed
into the parallel transmitter input bus. Data from the normal input source is ignored in PRBS mode. The PBRS
pattern is then fed through the transmitter circuitry as if it was normal data and sent out by the transmitter. The
output can be sent to a bit error rate tester (BERT) or to the receiver of another SLK2721 device. If an error
occurs in the PRBS pattern, the PRBSPASS pin is set low for two RXCLKP/N cycles.
Upon application of minimum valid power, the SLK2721 device generates a power-on reset. During the
power-on reset the PRXDATA[0:3] signal pins go to 3-state. RXCLKP and RXCLKN are held low. The length of
the power-on reset cycle is dependent upon the REFCLKP and REFCLKN frequency but is less than 1 ms in
duration.
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