PM5345S Datasheet, PDF (59/196 Pages) PMC-Sierra, Inc – SATURN USER NETWORK INTERFACE TELECOM STANDARD PRODUCT

DATA SHEET
PMC-930305
ISSUE 4
Figure 6 - Cell Delineation State Diagram
correct HCS
(byte by byte)
HUNT
Incorrect HCS
(cell by cell)
PM5345 S/UNI-155
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PRESYNC
ALPHA
consecutive
incorrect HCS's
(cell by cell)
SYNC
DELTA
consecutive
correct HCS's
(cell by cell)
The values of ALPHA and DELTA determine the robustness of the delineation
method. ALPHA determines the robustness against false misalignments due to
bit errors. DELTA determines the robustness against false delineation in the
synchronization process. ALPHA is chosen to be 7 and DELTA is chosen to be 6.
These values result in a maximum average time to delineate of 31 µs.
10.7.2 Descrambler
The self synchronous descrambler operates on the 48 byte cell payload only.
The circuitry descrambles the information field using the 'x43 + 1' polynomial.
The descrambler is disabled for the duration of the header and HCS fields, and
may optionally be disabled.
10.7.3 Cell Filter and HCS Verification
Cells are filtered (or dropped) based on HCS errors and/or a cell header pattern.
Cell filtering is optional and is enabled through the RACP registers. Cells are
passed to the receive FIFO while the cell delineation state machine is in the
SYNC state as described above. When both filtering and HCS checking are
enabled, cells are dropped if uncorrectable HCS errors are detected, or if the
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