XRT73R12_07 Datasheet, PDF (44/89 Pages) Exar Corporation – TWELVE CHANNEL E3/DS3/STS-1 LINE INTERFACE UNIT

XRT73R12
TWELVE CHANNEL E3/DS3/STS-1 LINE INTERFACE UNIT
REV. 1.0.2
6.0 DIAGNOSTIC FEATURES
6.1 PRBS Generator and Detector
The XRT73R12 contains an on-chip Pseudo Random Binary Sequence (PRBS) generator and detector for
diagnostic purpose. With the PRBSEN_n bit = “1”, the transmitter will send out PRBS of 2²³-1 in E3 rate or
2¹⁵-1 in STS-1/DS3 rate. At the same time, the receiver PRBS detector is also enabled. When the correct
PRBS pattern is detected by the receiver, the RNEG/LCV pin will go “Low” to indicate PRBS synchronization
has been achieved. When the PRBS detector is not in sync the PRBSLS bit will be set to “1” and RNEG/LCV
pin will go “High”.
With the PRBS mode enabled, the user can also insert a single bit error by toggling “INSPRBS” bit. This is
done by writing a “1” to INSPRBS bit. The receiver at RNEG/LCV pin will pulse “High” for one RxClk cycle for
every bit error detected. Any subsequent single bit error insertion must be done by first writing a “0” to
INSPRBS bit and followed by a “1”.
Figure 29 shows the status of RNEG/LCV pin when the XRT73R12 is configured in PRBS mode.
NOTE: In PRBS mode, the device is forced to operate in Single-Rail Mode.
FIGURE 29. PRBS MODE
RxClk
SYNC LOSS
RxNEG/LCV
PRBS SYNC
Single Bit Error
41