PM6341 E1XC
DATA SHEET
PMC-910419
ISSUE 8
E1 FRAMER/TRANSCEIVER
9.7
Elastic Store (ELST)
The Elastic Store function is provided by the ELST block.
The Elastic Store (ELST) block 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 backplane timing is derived from the receive line data (i.e. the RCLKO
output is used), the elastic store can be bypassed to eliminate the 2 frame delay.
In this configuration the elastic store can be used to measure frequency
differences between the recovered line clock and another 2.048 MHz clock
applied to the BRCLK input. A typical example might be to measure the
difference in frequency between two received T1 streams (i.e. East-West
frequency difference) by monitoring the number of SLIP occurrences of one
direction with respect to the other.
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.
To allow for the extraction of signalling information in the PCM data timeslots,
multiframe identification is also passed through the ELST.
9.8
Signalling Extractor (SIGX)
The Signalling Extraction function is provided by the Signalling Extractor (SIGX)
block. The TSB provides channel associated signalling (CAS) extraction from an
E1 signalling multiframe. Signalling data is extracted from timeslot (TS) 16 of
each frame within a signalling multiframe and buffered. The SIGX selectively
debounces the bits, and serializes the results onto the 2048 kbit/s serial stream
BRSIG output. Buffered signalling data is aligned with its associated voice
PROPRIETARY AND CONFIDENTIAL TO PMC-SIERRA, INC., AND FOR ITS CUSTOMERS’ INTERNAL USE
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PMC [ PMC-SIERRA, INC ]
