PM7346 S/UNI-QJET
DATASHEET
PMC-960835
ISSUE 6
SATURN QUAD USER NETWORK INTERFACE FOR J2, E3, T3
9
FUNCTIONAL DESCRIPTION
9.1 DS3 Framer
The DS3 Framer (T3-FRMR) Block integrates circuitry required for decoding a
B3ZS-encoded signal and framing to the resulting DS3 bit stream. The T3-FRMR
is directly compatible with the M23 and C-bit parity DS3 applications.
The T3-FRMR decodes a B3ZS-encoded signal and provides indications of line
code violations. The B3ZS decoding algorithm and the LCV definition can be
independently chosen through software. A loss of signal (LOS) defect is also
detected for B3ZS encoded streams. LOS is declared when inputs RPOS and
RNEG contain zeros for 175 consecutive RCLK cycles. LOS is removed when
the ones density on RPOS and/or RNEG is greater than 33% for 175 ±1 RCLK
cycles.
The framing algorithm examines five F-bit candidates simultaneously. When at
least one discrepancy has occurred in each candidate, the algorithm examines
the next set of five candidates. When a single F-bit candidate remains in a set,
the first bit in the supposed M-subframe is examined for the M-frame alignment
signal (i.e., the M-bits, M1, M2, and M3 are following the 010 pattern). Framing is
declared, and out-of-frame is removed, if the M-bits are correct for three
consecutive M-frames while no discrepancies have occurred in the F-bits. During
the examination of the M-bits, the X-bits and P-bits are ignored. The algorithm
gives a maximum average reframe time of 1.5 ms.
While the T3-FRMR is synchronized to the DS3 M-frame, the F-bit and M-bit
positions in the DS3 stream are examined. An out-of-frame defect is detected
when 3 F-bit errors out of 8 or 16 consecutive F-bits are observed (as selected
by the M3O8 bit in the DS3 FRMR Configuration Register), or when one or more
M-bit errors are detected in 3 out of 4 consecutive M-frames. The M-bit error
criteria for OOF can be disabled by the MBDIS bit in the DS3 Framer
Configuration register. The 3 out of 8 consecutive F-bits out-of-frame ratio
provides more robust operation, in the presence of a high bit error rate, than the
3 out of 16 consecutive F-bits ratio. Either out-of-frame criteria allows an out-of-
frame defect to be detected quickly when the M-subframe alignment patterns or,
optionally, when the M-frame alignment pattern is lost.
Also while in-frame, line code violations, M-bit or F-bit framing bit errors, and P-
bit parity errors are indicated. When C-bit parity mode is enabled, both C-bit
parity errors and far end block errors are indicated. These error indications, as
well as the line code violation and excessive zeros indication, are accumulated
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