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The DLOS detector supports the requirements of ANSI T1.231 for STS-1 LOS defects. At the STS-1 rate, the time
required for the DLOS detector to count 192 consecutive zeros falls in the range of 2.3
≤ T ≤ 100μs required by
ANSI T1.231 for declaring an LOS defect. Although the time required for the DLOS detector to count 192
consecutive pulse intervals with no excessive zeros is less than the 125
μs to 250μs period required by ANSI
T1.231 for clearing an LOS defect, a period of this length where LOS is inactive can easily be timed in software.
During LOS, the
RCLK output pin is derived from the LIU’s reference clock. The ALOS detector has a longer time
constant than the DLOS detector. Thus, when the incoming signal is lost, the DLOS detector activates first
(asserting the
RLOS pin and LOS status bit), followed by the ALOS detector. When a signal is restored, the DLOS
detector does not get a valid signal that it can qualify for no EXZ occurrences until the ALOS detector has seen the
signal rise above a signal level approximately 22dB below nominal.
8.3.6 Framer Interface Format and the B3ZS/HDB3 Decoder
The recovered data can be output in either bipolar or binary format. Reception of a B3ZS or HDB3 codeword is
8.3.6.1
Bipolar Interface Format
To select the bipolar interface format, pull the
RBIN pin low and clear the
PORT.CR2:RBIN configuration bit. In
bipolar format, the B3ZS/HDB3 decoder is disabled and the recovered data is buffered and output on the
RPOSand
RNEG outputs for subsequent decoding by a downstream framer or mapper. Received positive-polarity pulses
are indicated by
RPOS = 1, while negative-polarity pulses are indicated by
RNEG = 1.
In DS3 and STS-1 modes an excessive zeros error (EXZ) is declared whenever there is an occurrence of 3 or
more zeros in a row in the receive data stream. In E3 mode, an EXZ error is declared whenever there is an
occurrence of 4 or more zeros. EXZs are flagged by the
LINE.RSRL:EXZL and EXZCL latched status bits and
In all three modes (DS3, E3, and STS-1) a bipolar violation is declared if two positive pulses are received without
an intervening negative pulse or if two negative pulses are received without an intervening positive pulse. Bipolar
violations (BPVs) are flagged by the
LINE.RSRL:BPVL and BPVCL latched status bits and accumulated in the
8.3.6.2
Binary Interface Format
To select the binary interface format, pull the
RBIN pin high (all ports) or set the
PORT.CR2:RBIN configuration bit
(per port). In binary format, the B3ZS/HBD3 decoder is enabled, and the recovered data is decoded and output as
a binary (NRZ) value on the
RDAT pin, while bipolar violations, code violations, and excessive zero errors are
detected and flagged on the
RLCV pin.
In DS3 and STS-1 modes, B3ZS decoding is performed. In these modes, whenever a B3ZS codeword is found in
the receive data stream it is replaced with three zeros. In E3 mode HDB3 decoding is performed. In this mode,
whenever an HDB3 codeword is found in the receive data stream it is replaced with four zeros. The decoding
search criteria for a B3ZS/HDB3 codeword is programmable using the
LINE.RCR:RDZSF control bit.
An excessive zeros error (EXZ) is declared in DS3 and STS-1 modes whenever there is an occurrence of 3 or
more zeros in a row in the receive data stream. In E3 mode, an EXZ error is declared whenever there is an
occurrence of 4 or more zeros in a row. EXZs are flagged by the
LINE.RSRL:EXZL and EXZCL latched status bits
A bipolar violation error (BPV error) is declared in DS3 and STS-1 modes if a BPV is detected that is not part of a
valid B3ZS codeword. In E3 mode, a bipolar violation error is declared whenever a BPV is detected that is not part
of a valid HDB3 codeword. In E3 mode if
LINE.RCR:E3CVE = 1, code violations are detected rather than bipolar
violation errors. A code violation is declared whenever consecutive BPVs (not BPV errors) have the same polarity
(ITU O.161 definition). The error detection search criteria for a B3ZS/HDB3 codeword is programmable using the
LINE.RCR:REZSF control bit. Bipolar violations (or code violations if
LINE.RCR:E3CVE = 1) are flagged by the
In the discussion that follows, a valid pulse that conforms to the AMI rule is denoted as B. A BPV pulse that violates
the AMI rule is denoted as V.
In DS3 and STS-1 modes, B3ZS decoding is performed, and
RLCV is asserted during any
RCLK cycle where the
data
RDAT causes ones of the following code violations: