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Multi-Service Access Device For Channelized Interfaces
Telecom Standard Product Data Sheet
Production
Proprietary and Confidential to PMC-Sierra, Inc., and for its Customers’ Internal Use
Document ID: PMC-1990823, Issue 4
93
DS3 Serializer
Incoming DS3 ATM or packet data is sampled from the TCAS-12 block, deserialized and written
into the Elastic Store. The DS3 clock rate is taken from the DS3TICLK input pin of the S/UNI-
MACH48.
Elastic Store
The elastic store block is provided to compensate for frequency differences between the DS-3
stream (DS3TICLK) and the STS-1 (STM-0/AU3) SPE capacity (SYSCLK). The DS3 Serializer
writes data into the elastic store at the DS3TICLK/8 rate while data is read out at the stuffed
STS-1 (STM-0/AU3) byte rate. If an overflow or underflow condition occurs, an interrupt is
optionally asserted and the Elastic Store read and write address are reset to the startup values
(logically 180 degrees apart).
DS3 Synchronizer
The DS3 Synchronizer performs the mapping of the DS3 into the STS-1 (STM-0/AU3) SPE. The
DS3 Synchronizer monitors the Elastic Store level to control the stuffing algorithm to avoid
overflow (i.e. run faster) and underflow (i.e. run slower) conditions. The fill level of the elastic
store is monitored and stuff opportunities in the DS3 mapping are used to center the Elastic Store.
To consume a stuff opportunity, the five C-bits on a row are set to ones and the S bit is used to
carry an DS3 information bit. When the S bit is not used to carry information, the C-bits on the
row are set to zeros.
11.20 DS3 Transmitter (DS3-TRAN)
The DS3 Transmitter (DS3-TRAN) Block integrates circuitry required to insert the overhead bits
into a DS3 bit stream. The DS3-TRAN is directly compatible with C-bit parity DS3 formats.
Status signals such as far end receive failure (FERF), the alarm indication signal, and the idle
signal can be inserted when their transmission is enabled by internal register bits. FERF can also
be automatically inserted on detection of any combination of OOF or RED, or AIS by the
DS3-FRMR.
A valid pair of P-bits is automatically calculated and inserted by the DS3-TRAN. When C-bit
parity mode is selected, the path parity bits, and far end block error (FEBE) indications are
automatically inserted.
When enabled for C-bit parity operation, the FEAC channel is sourced by the XBOC bit-oriented
code transmitter. The path maintenance data link messages are sourced by the TDPR data link
transmitter. These overhead signals can also be overwritten by using the TOH and TOHINS
inputs.
The DS3-TRAN supports diagnostic modes in which it inserts parity or path parity errors, F-bit
framing errors, M-bit framing errors, invalid X or P-bits, line code violations, or all-zeros.