PM6341 datasheet(67/272 Pages) PMC

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PM6341 E1XC

DATA SHEET

PMC-910419

ISSUE 8

E1 FRAMER/TRANSCEIVER

PROPRIETARY AND CONFIDENTIAL TO PMC-SIERRA, INC., AND FOR ITS CUSTOMERS’ INTERNAL USE

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

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