PM4388 Datasheet, PDF (36/284 Pages) PMC-Sierra, Inc – Octal T1 Framer

DATA SHEET
PMC-960840
ISSUE 5
PM4388 TOCTL
OCTAL T1 FRAMER
9 FUNCTIONAL DESCRIPTION
9.1 Framer (FRMR)
The framing function is provided by the FRMR block. This block searches for the
framing bit position in the ingress stream. It works in conjunction with the FRAM
block to search for the framing bit pattern in the standard superframe (SF), or
extended superframe (ESF) framing formats. When searching for frame, the
FRMR simultaneously examines each of the 193 (SF) or each of the 772 (ESF)
framing bit candidates. The FRAM block is addressed and controlled by the
FRMR while frame synchronization is acquired.
The time required to acquire frame alignment to an error-free ingress stream,
containing randomly distributed channel data (i.e. each bit in the channel data
has a 50% probability of being 1 or 0), is dependent upon the framing format.
For SF format, the FRMR block will determine frame alignment within 4.4ms 99
times out of 100. For ESF format, the FRMR will determine frame alignment
within 15 ms 99 times out of 100.
Once the FRMR has found frame, the ingress data is continuously monitored for
framing bit errors, bit error events (a framing bit error in SF or a CRC-6 error in
ESF), and severely errored framing events. The FRMR also detects out-of-frame,
based on a selectable ratio of framing bit errors.
The FRMR can also be disabled to allow reception of unframed data. While the
FRMR is disabled, control of the FRAM block is relinquished for use as the
elastic store.
9.2 Framer/Slip Buffer RAM (FRAM)
The Framer/Slip Buffer RAM function is provided by the Framer RAM (FRAM)
block. The FRAM is used to store up to 4 frames of data while the FRMR is
acquiring frame and up to 2 frames of data during normal operation (i.e. when
accessed by Elastic Store). The FRAM is shared between the Elastic Store
(ELST) and the FRMR: when frame synchronization is lost, the FRMR takes
control of the FRAM and uses it to find frame; when frame synchronization is
determined, the FRMR relinquishes control of FRAM to ELST which buffers the
incoming PCM data.
PROPRIETARY AND CONFIDENTIAL TO PMC-SIERRA, INC., AND FOR ITS CUSTOMERS’ INTERNAL USE
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