XRT75R12 Datasheet, PDF(81/89 Page) Exar Corporation – TWELVE CHANNEL E3/DS3/STS-1 LINE INTERFACE UNIT WITH JITTER ATTENUATOR

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XRT75R12 Datasheet, PDF (81/89 Pages) Exar Corporation – TWELVE CHANNEL E3/DS3/STS-1 LINE INTERFACE UNIT WITH JITTER ATTENUATOR

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PRELIMINARY

TWELVE CHANNEL E3/DS3/STS-1 LINE INTERFACE UNIT WITH JITTER ATTENUATOR

XRT75R12

REV. P1.0.2

BIT NUMBER

7-6

NAME

Reserved

PRBS Enable

RLB_n

TYPE

DESCRIPTION

R/W PRBS Generator and Receiver Enable - Channel_n:

This READ/WRITE bit-field is used to enable or disable the PRBS

Generator and Receiver within a given Channel of the XRT75R12.

If the user enables the PRBS Generator and Receiver, then the follow-

ing will happen.

1. The PRBS Generator (which resides within the Transmit Section

of the Channel) will begin to generate an unframed, 2^15-1

PRBS Pattern (for DS3 and STS-1 applications) and an

unframed, 2^23-1 PRBS Pattern (for E3 applications).

2. The PRBS Receiver (which resides within the Receive Section

of the Channel) will now be enabled and will begin to search the

incoming data for the above-mentioned PRBS patterns.

0 - Disables both the PRBS Generator and PRBS Receiver within the

corresponding channel.

1 - Enables both the PRBS Generator and PRBS Receiver within the

corresponding channel.

NOTES:

1. To check and monitor PRBS Bit Errors, DR (Dual Rail) mode

will be over-ridden and Single Rail mode forced for the

duration of this mode. This will configure the RNEG/LCV_n

output pin to function as a PRBS Error Indicator. All errors

will be flagged on this pin. The errors will also be

accumulated in the 16 bit Error counter for the channel.

2. If the user enables the PRBS Generator and PRBS Receiver,

the Channel will ignore the data that is being accepted from

the System-side Equipment (via the TxPOS_n and TxNEG_n

input pins) and will overwrite this outbound data with the

PRBS Pattern.

3. The system must provide an accurate and stable data-rate

clock to the TxClk_n pin during this operation.

R/W Loop-Back Select - RLB Bit - Channel_n:

This READ/WRITE bit-field along with the corresponding LLB_n bit-

field is used to configure a given channel into various loop-back modes

ass shown by the following table.

LLB_n

RLB_n

Loop-back Mode

Normal (No Loop-back) Mode

Remote Loop-back Mode

Analog Local Loop-back Mode

Digital Local Loop-back Mode

LLB_n

R/W Loop-Back Select - LLB Bit-field - Channel_n:

See the table (above) for RLB_n.

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