RELEASED
PM4354 COMET-QUAD
DATASHEET
PMC-1990315
ISSUE 6
FOUR CHANNEL COMBINED E1/T1/J1
TRANSCEIVER / FRAMER
PROPRIETARY AND CONFIDENTIAL TO PMC-SIERRA, INC. AND FOR ITS CUSTOMERS’ INTERNAL USE
58
9.21 Transmit Elastic Store (TX-ELST)
The Transmit Elastic Store (TX-ELST) provides the ability to decouple the line timing from the
backplane timing. The TX-ELST is required whenever the backplane and lineside clocks are not
traceable to a common source.
When the elastic store is being used, if the average frequency of the backplane data is greater
than the average frequency of the line clock, the buffer will fill. Under this condition a controlled
slip will occur upon the next frame boundary. The following frame of PCM data will be deleted.
If the average frequency of the backplane data is less than the average frequency of the line
clock, the buffer will empty. Under this condition a controlled slip will occur upon the next frame
boundary. The last frame will be repeated.
A slip operation is always performed on a frame boundary. The TX-ELST is upstream of the
frame overhead insertion; therefore, frame slips do not corrupt the frame alignment signal.
When the line timing is derived from CTCLK or BTCLK is an output, the elastic store is bypassed
to eliminate the one frame delay.
9.22 T1 Basic Transmitter (T1-XBAS)
The T1 Basic Transmitter (T1-XBAS) block generates the 1.544 Mbit/s T1 data stream according
to SF or ESF frame formats.
In concert with the Transmit Per-Channel Serial Controller (TPSC), the T1-XBAS block, provides
per-channel control of idle code substitution, data inversion (either all 8 bits, sign bit magnitude or
magnitude only), and zero code suppression. Three types of zero code suppression (GTE, Bell
and "jammed bit 8") are supported and selected on a per-channel basis to provide minimum ones
density control. An internal signaling control stream provides per-channel control of robbed bit
signaling and selection of the signaling source. All channels can be forced into a trunk
conditioning state (idle code substitution and signaling conditioning) by use of the Master Trunk
Conditioning bit in the Configuration Register.
A data link is provided for ESF mode. The data link sources include bit oriented codes and HDLC
messages. Support is provided for the transmission of framed or unframed Inband Code
sequences and transmission of AIS or Yellow alarm signals for all formats.
The transmitter can be disabled for framing via the disable bit in the Transmit Functions Enable
register. When transmitting ESF formatted data, the framing bit, datalink bit, or the CRC-6 bit from
the backplane transmit stream can be by-passed to the output PCM stream. Finally, the
transmitter can be by-passed completely to provide an unframed operating mode.