PM6344 datasheet(52/256 Pages) PMC

52 / 256 page

STANDARD PRODUCT

PMC-Sierra, Inc.

PM6344 EQUAD

PMC-951013

ISSUE 5

QUADRUPLE E1 FRAMER

When the internal HDLC receiver is disabled, the serial data extracted by the

FRMR block is output on the RDLSIG[x] pin and is updated on the falling clock

edge of the RDLCLK[x] pin.

8.6

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[x[ 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 E1 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 signaling information in the PCM data timeslots,

multiframe identification is also passed through the ELST.

8.7

Signaling Extractor (SIGX)

The Signaling Extraction function is provided by the Signaling Extractor (SIGX)

block. The block provides channel associated signaling (CAS) extraction from an

E1 signaling multiframe. Signaling data is extracted from timeslot 16 of each

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