XRT72L50 Datasheet, PDF (395/471 Pages) Exar Corporation – SINGLE CHANNEL DS3/E3 FRAMER IC WITH HDLC CONTROLLER

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XRT72L50
SINGLE CHANNEL DS3/E3 FRAMER WITH HDLC CONTROLLER
REV. 1.2.1
Handling of data from the Internal Overhead Bit Generator
By default, the Transmit E3 Framer block will internally generate the overhead bytes. However, if the Terminal
Equipment inserts its own values for the overhead bits or bytes (via the Transmit Overhead Data Input
Interface) or, if the user enables and employs the Transmit E3 HDLC Controller block, then these internally
generated overhead bytes will be overwritten.
Handling of data from the Transmit Overhead Data Input Interface
For E3 applications, the Transmit E3 Framer block automatically generates and inserts the framing alignment
bytes (e.g., the FA1 and FA2 framing alignment bytes) into the Outbound E3 frames. Further, the Transmit E3
Framer block will automatically compute 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 Interface 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 following 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 processing.
Figure 165 presents a simple illustration of the Transmit E3 Framer block, along with the associated paths to
the other functional blocks within the chip.
FIGURE 165. THE TRANSMIT E3 FRAMER BLOCK AND THE ASSOCIATED PATHS TO OTHER FUNCTIONAL BLOCKS
Transmit HDLC
Controller/Buffer
Transmit Overhead
Data Input Interface
Transmit Payload Data
Input Interface
Transmit
E3 Framer
Block
To Transmit E3 LIU
Interface Block
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