STANDARD PRODUCT
PM4351 COMET
DATA SHEET
PMC-1970624
ISSUE 10
COMBINED E1/T1 TRANSCEIVER
have been present for 1.5 sec (± 100 ms); the AIS alarm is removed when the
AIS condition has been absent for 16.8 sec (± 500 ms).
-3
CFA alarm detection algorithms operate in the presence of a random 10 bit
error rate.
The ALMI also indicates the presence or absence of the Yellow, Red, and AIS
alarm signal conditions over 40 ms , 40 ms and 60 ms intervals, respectively,
allowing an external microprocessor to integrate the alarm conditions via
software with any user-specific algorithms. Alarm indication is provided through
internal register bits.
9.11 Receive Elastic Store (RX-ELST)
The Receive Elastic Store (RX-ELST) synchronizes incoming PCM frames to the
local backplane clock, BRCLK. The frame data is buffered in a two-frame
circular data buffer. Input data is written to the buffer using a write pointer and
output data is read from the buffer using a read pointer.
When the elastic store is being used, if the average frequency of the incoming
data is greater than the average frequency of the backplane clock, the write
pointer will catch up to the read pointer and the buffer will be filled. Under this
condition a controlled slip will occur when the read pointer crosses the next
frame boundary. The following frame of PCM data will be deleted.
If the average frequency of the incoming data is less than the average frequency
of the backplane clock, the read pointer will catch up to the write pointer and the
buffer will be empty. Under this condition a controlled slip will occur when the
read pointer crosses the next frame boundary. The last frame which was read
will be repeated.
A slip operation is always performed on a frame boundary.
When the backplane timing is derived from the receive line data (i.e. BRCLK is
an output), the elastic store can be bypassed to eliminate the two frame delay.
In this configuration the elastic store can be used to measure frequency
differences between the recovered line clock and another 1.544 MHz or
2.048 MHz clock applied to the BRCLK input. A typical example might be to
measure the difference in frequency between two received streams (i.e. East-
West frequency difference) by monitoring the number of SLIP occurrences of
one direction with respect to the other.
To allow for the extraction of signaling information in the PCM data channels,
superframe identification is also passed through the RX-ELST.
PROPRIETARY AND CONFIDENTIAL
50
PMC [ PMC-SIERRA, INC ]
