SLK2501

OC48/24/12/3 SONET/SDH MULTIRATE TRANSCEIVER

SLLS502A – OCTOBER 2001 – REVISED NOVEMBER 2001

12

POST OFFICE BOX 655303

detailed description (continued)

1:4 Serial to

Parallel

4:1 Parallel to

Serial

RXDATA (3–0)

RXCLK

TXDATA (3–0)

TXCLK

2.488 GHz

PLL

D

D

SRXDIP

SRXDIN

LLOOP

STXDOP

STXDON

Recovered Clock

Figure 4. Local Loopback Data Path

remote loopback

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.

1:4 Serial to

Parallel

4:1 Parallel to

Serial

RXDATA (3–0)

RXCLK

2.488 GHz

PLL

D

D

SRXDIP

SRXDIN

LLOOP

STXDOP

STXDON

Recovered Clock

Figure 5. Remote Loopback Data Path/Repeater Mode Operation

PRBS

The SLK2501 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 SLK2501. If an error occurs

in the PRBS pattern, the PRBSPASS pin is set low for two RXCLKP/N cycles.