STANDARD PRODUCT
PM4328 TECT3
DATASHEET
PMC-2011596
ISSUE 1
HIGH DENSITY T1/E1 FRAMER
AND M13 MULTIPLEXER
9.7 Elastic Store (ELST)
The Elastic Store (ELST) synchronizes ingress frames to the common ingress
clock and frame pulse (CICLK, CIFP) in the Clock Slave ingress modes or to the
common ingress H-MVIP clock and frame pulse (CMV8MCLK, CMVFP,
CMVFPC) in H-MVIP modes. 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 subsequent ingress frame is 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 previous ingress frame is
repeated.
A slip operation is always performed on a frame boundary.
When the ingress timing is recovered from the receive data the elastic store can
be bypassed to eliminate the 2 frame delay. In this configuration (the Clock
Master ingress modes), the elastic store is used to synchronize the ingress
frames to the transmit line clock so that per-DS0 loopbacks may be enabled.
To allow for the extraction of signaling information in the data channels,
superframe identification is also passed through the ELST.
For payload conditioning, the ELST may optionally insert a programmable idle
code into all channels when the framer is out of frame synchronization. This
code is set to all 1’s when the ELST is reset.
If the data is required to pass through the TECT3 unchanged during an out-of-
frame condition, then the elastic store may be bypassed.
9.8 Signaling Elastic Stores (RX-SIG-ELST and TX_SIG-ELST)
There are two additional elastic stores used to adapt the differences in rate
between the CAS or CCS H-MVIP signaling rates and the serial clock and data
or SBI data rates when in simultaneous SBI or serial clock and data with
PROPRIETARY AND CONFIDENTIAL
65
PMC [ PMC-SIERRA, INC ]
