PM5366-PI PMC-Sierra, Inc., PM5366-PI Datasheet - Page 117

• Manufacturer Part Number: PM5366-PI
• Description: HIGH DENSITY 84/63 CHANNEL VT/TU MAPPER AND M13 MULTIPLEXER
• Manufacturer: PMC-Sierra, Inc.

PRELIMINARY
DATASHEET
PMC-2010672
9.27.3 DS3 Desynchronizer
PROPRIETARY AND CONFIDENTIAL
optionally asserted and the Elastic Store read and write address are reset to the
startup values (logically 180 degrees apart).
The Desynchronizer monitors the Elastic Store level to control the de-stuffing
algorithm to avoid overflow and underflow conditions. The Desynchronizer
assumes either a 51.84 MHz clock or a 44.928 MHz clock (provided via input
CLK52M).
When using a 44.928 MHz CLK52M clock, the DS3 clock is generated using a
fixed 8 KHz interval. The 8KHz interval is subdivided into 9 rows. Each row
contains either 621 or 622 clock periods. The CLK52M contains 624 cycles per
row. To generate 621 pulses, a gap pattern of 207 clocks + 1 clock gap + 207
clocks + 1 clock gap + 207 clocks + 1 clock gap is used. To generate 622
pulses, a gap pattern of 207 clocks + 1 clock gap + 207 clocks + 1 clock gap +
208 clocks is used.
When using a 51.84 MHz CLK52M clock, the DS3 clock is generated using
similar gapping patterns. To generate 621 pulses per row, a gapping pattern of
63 * (7 clocks + 1 clock gap) + 36 * (5 clocks + 1 clock gap) is used. To generate
622 pulses per row, a gapping pattern of 63 * (7 clocks + 1 clock gap) + 35 * (5
clocks + 1 clock gap) + 6 clocks) is used.
Table 7 illustrates the gap patterns used to generate the desynchronized DS3
clock under the normal, DS3 AIS, faster and slower status. The faster pattern is
used to drain the elastic store to avoid overflows. The slower pattern is used to
allow the elastic store to fill to avoid underflows.
ISSUE 1
105
HIGH DENSITY 84/63 CHANNEL VT/TU MAPPER
AND M13 MULTIPLEXER
PM5366 TEMAP-84