PM8313 datasheet(44/192 Pages) PMC

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PM8313 D3MX

DATA SHEET

PMC-920702

ISSUE 5

M13 MULTIPLEXER

FUNCTIONAL DESCRIPTION

8.1

DS3 Framer

The DS3 Framer (FRMR) Block integrates circuitry required for decoding a

B3ZS-encoded signal and framing to the resulting DS3 bit stream. The FRMR is

directly compatible with the M23 and C-bit parity DS3 applications.

The FRMR decodes a B3ZS-encoded signal and provides indications of line

code violations. The B3ZS decoding algorithm and the LCV definition can

independently be chosen via software. Loss of signal is also detected.

The framing algorithm examines five F-bit candidates simultaneously. When at

least one discrepancy has occurred in all the candidates, the algorithm examines

the next set of 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,M3, are following the 010 pattern). Framing is

declared 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 less than 1.5 ms.

Once in-frame, the FRMR provides indications of the M-frame and M-subframe

boundaries, and identifies the overhead bit positions in the incoming DS3 signal.

While the FRMR is in-frame, the F-bit and M-bit positions in the DS3 stream are

examined. Out-of-frame is declared when 3 F-bit errors out of 16 consecutive F-

bits or 8 consecutive F-bits are observed (selectable by the M3O8 bit), 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 via 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 10-3 bit error rate than the 3

out of 16 consecutive F-bits ratio (less than one false OOF every minute verses

one false OOF every 6 seconds, respectively); either choice of out-of-frame ratios

allows an out-of-frame to be declared quickly when the M-subframe alignment

patterns or, optionally, when the M-frame alignment is lost.

Also while in-frame, 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, may be accumulated over 1 second

intervals with the T3 Performance Monitor (PMON). Note that the framer is an

PM8313 Datasheet(PDF) 44 Page - PMC-Sierra, Inc