PM7346 S/UNI-QJET
DATASHEET
PMC-960835
ISSUE 6
SATURN QUAD USER NETWORK INTERFACE FOR J2, E3, T3
Figure 9
- Framing Algorithm (CRC_REFR = 1)
Reset
or
Out of Fram e
Else
Slip 1 bit
Framing
Pattern
Matched
Mark multiframe alignment
Fail
Confirm Framing Pattern
in next m ultiframe
Pass
Fail
Fail
Fail
Check CRC-5 Sequence
Pass
Confirm Framing Pattern
in next m ultiframe
Pass
Check CRC-5 Sequence
Pass
Declare in-frame
Using this algorithm, the J2-FRMR will find frame in 10.22ms, on average when
starting the search in the worst possible position, given a 10-4 error rate and no
static mimic patterns. The algorithm will reject 99.90% of mimic patterns.
Further protection against mimic patterns is available by monitoring the rate of
CRC-5 errors.
Once frame alignment is found, the block sets the LOF indication low, indicates a
change of frame alignment (if it occurred). The block declares loss of frame
alignment if 7 consecutive FASs have been received in error. In the presence of
-3
a random 10 bit error rate the frame loss criteria provides a mean time to
falsely lose frame alignment of 1.65 years. The Frame Find Block can be forced
to initiate a frame search at any time when the REFRAME bit in the J2-FRMR
Configuration. Conversely, when the FLOCK bit is set to logic 1, the J2-FRMR
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