XRT72L71 Datasheet, PDF (42/102 Pages) Exar Corporation – DS3 ATM UNI/CLEAR CHANNEL FRAMER

XRT72L71
DS3 ATM UNI/CLEAR CHANNEL FRAMER
REV. 1.1.0
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• Additionally, the Transmit DS3 Framer can transmit
path maintenance data link messages to the
Remote Terminal Equipment via the on-chip LAPD
Transmitter.
• Generates interrupts upon “Completion of Trans-
mission of LAPD and FEAC” Messages.
Note: The Transmit DS3 Framer will support either M13 or
C-bit Parity Framing Formats.
CLEAR-CHANNEL-FRAMING MODE OF OPERA-
TION
When the XRT72L71has been configured to operate
in the “Clear-Channel Framer” mode, it can be func-
tionally subdivided into 6 different sections.
• Receive Section
• Transmit Section
• Microprocessor Interface Section
• Performance Monitor Section
• Test and Diagnostic Section
• Line Interface Unit Scan/Drive Section.
The features of each of the “Receive” and “Transmit”
Section (for Clear-Channel Framer applications) are
listed below.
THE RECEIVE SECTION
The purpose of the Receive Section of the XRT72L71
Clear-Channel DS3 Framer is to allow a given Termi-
nal to receive data from a remote terminal, which is
being transported over a DS3 data stream.
The Receive Section of the XRT72L71 Clear-Channel
DS3 Framer IC consists of the following functional
blocks.
• Receive DS3 Framer block
• Receive Overhead Data Output Interface block
• Receive Payload Data Output Interface block
It should be noted that the “Receive DS3 Framer”
block is also active, when the XRT72L71 has been
configured to operate in the “ATM UNI” Mode.
Each of these functional blocks, within the Receive
Section of the Framer will do the following.
• The Receive DS3 Framer block will synchronize to
the incoming DS3 data stream. All “inbound” DS3
data will be routed to the “Receive Payload Data
Output Interface” block. All overhead bits (which
are extracted from each “inbound” DS3 frame) will
be routed to the “Receive Overhead Data Output
Interface” block.
• The Receive DS3 Framer block can also be used to
receive FEAC (Far-End-Alarm & Control) mes-
sages and PMDL (Path Maintenance Data Link)
messages via the “on-chip” Receive HDLC Control-
ler block.
• The Receive Overhead Output Interface block out-
puts all overhead bits, which have been received
via the “inbound” DS3 data stream. The purpose of
the “Receive Overhead Output Interface” block is to
permit external circuitry (within the local terminal
equipment) to have access to these overhead bits,
for additional processing.
• The Receive Payload Data Output Interface block
outputs all data bits which have been received via
the XRT72L71, to the local terminal equipment.
Since the “Receive Payload Data Output Interface”
block outputs both “payload” and “overhead” data
bits, to the local terminal equipment; the “Receive
Payload Data Output Interface” block also includes
an “Overhead Indicator” output pin. This output pin
pulses “High” whenever an overhead bit is being
output via the “Receive Payload Data Output Inter-
face” block.
THE TRANSMIT SECTION
The purpose of the Transmit Section of the
XRT72L71 Clear-Channel DS3 Framer is to allow a
local terminal to transmit data to a remote terminal
equipment, via a DS3 transport medium.
The Transmit Section of the XRT72L71 Clear-Chan-
nel DS3 Framer consists of the following functional
blocks.
• Transmit Payload Data Input Interface block
• Transmit Overhead Data Input Interface block
• Transmit DS3 Framer block
It should be noted that the “Transmit DS3 Framer”
block is also active, whenever the XRT72L71 has
been configured to operate in the “ATM UNI” Mode.
The Transmit Section of the Clear-Channel DS3
Framer will:
• Accept all “user” data, (which is required to be
transported to the Remote Terminal Equipment via
a DS3 data stream) via the “Transmit Payload Data
Input Interface block.
• Optionally accepts and insert overhead bits (into
the “outbound” DS3 data-stream) via the “Transmit
Overhead Input Interface block.
• The Transmit DS3 Framer block will accept payload
data (from the Transmit Payload Data Input Inter-
face block) and overhead data (from the Transmit
Overhead Data Input Interface block) and will cre-
ate a DS3 data stream. If no overhead data is
inserted via the “Transmit Overhead Data Input
interface” block, then the “Transmit DS3 Framer”
block will insert its own values for the overhead bits.
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