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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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