XRT74L73 Datasheet, PDF (123/488 Pages) Exar Corporation – 3 CHANNEL, ATM UNI/PPP DS3/E3 FRAMING CONTROLLER

PRELIMINARY
XRT74L73
3 CHANNEL, ATM UNI/PPP DS3/E3 FRAMING CONTROLLER
REV. P1.0.1
Final Notes about the Transmit PLCP Processor
The Transmit PLCP Processor will be disabled, upon
power up or reset. Therefore, a “1” must be written to
this bit in order to enable the PLCP Processor. Selec-
tion of this bit affects both the Transmit PLCP Proces-
sor and the Receive PLCP Processor.
The advantage of selecting the “Direct-Mapped ATM”
option is to result in a more efficient use of the DS3
Bandwidth. This is because in the Direct Mapped
ATM mode, it is not required to include all of the POH
bytes that must be included in PLCP frames.
The Transmit PLCP Processor will inform the external
circuitry that a PLCP frame has been assembled and
transmitted out of the PLCP Processor by pulsing the
TxPFrame output pin ‘high’ during the transmission of
the last trailer nibble.
2.4Transmit DS3 Framer
2.4.1Brief Description of the Transmit DS3 Framer
The Transmit DS3 Framer takes the incoming data,
which can be either PLCP frames from the Transmit
PLCP Processor or ATM Cells from the Transmit Cell
Processor and maps it into the payload portion of the
DS3 frame. The Transmit DS3 Framer supports either
the M13 or C-Bit Parity frame formats. The Transmit
DS3 Framer operates at 44.736 MHz and framing is
derived from an input clock signal. The framing over-
head bits are generated and inserted with the DS3
payload bits to make up the complete DS3 frame. The
DS3 frame is then encoded into either the Unipolar, AMI
or B3ZS line codes. When the Transmit DS3 Framer is
operating in the C-Bit Parity Framing format, it provides
an interface that supports the transmission of path
maintenance data link messages on the outgoing DS3
frames via the on-chip LAPD Transmitter. The Transmit
DS3 Framer also includes an on-chip Transmit FEAC
Processor that supports the transmission of FEAC (Far
End Alarm and Control) messages over the outgoing
DS3 frame. Different transmission conditions like AIS
(Alarm Indication Signal), Idle Condition and the Yellow
Alarm can be generated upon software command.
Further, the LOS (Loss of Signal) condition can be
simulated upon software command.
2.5 TRANSMIT E3 FRAMER
2.5.1 Brief Description of the Tansmit E3
Framer
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