XRT74L73 Datasheet, PDF (421/488 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
For E3 applications, the Transmit E3 Framer block
automatically generates and inserts the framing align-
ment bytes (e.g., the "FA1” and “FA2” framing align-
ment bytes) into the Outbound E3 frames. Further,
the Transmit E3 Framer block will automatically com-
pute and insert the EM byte into the Outbound E3
frames. Hence, the Transmit E3 Framer block will not
accept data from the Transmit OH Data Input Inter-
face block for the "FA1”, “FA2” and “EM” bytes.
However, the Transmit E3 Framer block will accept
(and insert) data from the Transmit Overhead Data
Input Interface for the following byte-fields.
• MA byte
• TR byte
• NR byte
• GC byte
If the user’s local Data Link Equipment activates the
Transmit Overhead Data Input Interface block and
writes data into this interface for these bits or bytes,
then the Transmit E3 Framer block will insert this data
into the appropriate overhead bit/byte-fields, within
the Outbound E3 frames.
6.2.4.2 Detailed Functional Description of the
Transmit E3 Framer Block
The Transmit E3 Framer receives data from the fol-
lowing three sources and combines them together to
form a E3 data stream.
• The Transmit Payload Data Input Interface block.
• The Transmit Overhead Data Input Interface block
• The Transmit HDLC Controller block.
Afterwards, this E3 data stream will be routed to the
Transmit E3 LIU Interface block, for further process-
ing.
Figure 184 presents a simple illustration of the
Transmit E3 Framer block, along with the associated
paths to the other functional blocks within the chip.
FIGURE 184. THE TRANSMIT E3 FRAMER BLOCK AND THE ASSOCIATED PATHS TO OTHER FUNCTIONAL BLOCKS
Transmit HDLC
Controller/Buffer
Transmit Overhead
Data Input Interface
Transmit
E3 Framer
Block
To Transmit E3 LIU
Interface Block
Transmit Payload
Data Input Interface
In addition to taking data from multiple sources and
multiplexing them, in appropriate manner, to create
the Outbound E3 frames, the Transmit E3 Framer
block has the following roles.
• Generating Alarm Conditions
• Generating Errored Frames (for testing purposes)
• Routing Outbound E3 frames to the Transmit E3
LIU Interface block
Each of these additional roles are discussed below.
6.2.4.2.1 Generating Alarm Conditions
The Transmit E3 Framer block permits the user to, by
writing the appropriate data into the on-chip registers,
to override the data that is being written into the
Transmit Payload Data and Overhead Data Input In-
terfaces and transmit the following alarm conditions.
• Generate the Yellow Alarms (or FERF indicators)
• Manipulate the FERF-bit, within the MA byte (set
them to "0")
• Generate the AIS Pattern
• Generate the LOS pattern
• Generate FERF (Yellow) Alarms, in response to
detection of a Red Alarm condition (via the Receive
Section of the XRT74L73).
• Generate and transmit a desired value for the
FEBE (Far-End-Block Error) bit, within the MA byte.
The procedure and results of generating any of these
alarm conditions is presented below.
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