XRT72L50 Datasheet, PDF (289/471 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 Transmit Payload Data Input Interface
For E3 applications, all data that is input to the Transmit Payload Data Input Interface will be inserted into the
payload bit positions within the outbound E3 frames.
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 10 bit FAS framing alignment signal) 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 FAS signal.
However, the Transmit E3 Framer block will accept (and insert) data from the Transmit Overhead Data Input
Interface for both the A and N bit-fields.
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.
Handling of data from the Transmit HDLC Controller Block
The exact manner in how the Transmit E3 Framer handles data from the Transmit HDLC Controller block
depends upon whether the Transmit HDLC Controller is activated or not. If the Transmit DS3 HDLC Controller
block is not activated, then the Transmit E3 Framer block will insert a “1” into each N bit-field, within each
outbound E3 frame.
If the Transmit E3 HDLC Controller block is activated, then data will be inserted into the N bit-fields as
described in Section 4.2.3.
5.2.4.2 Detailed Functional Description of the Transmit E3 Framer Block
The Transmit E3 Framer receives data from the following four sources and combines them together to form the
E3 data stream.
• The Transmit Payload Data Input Interface block.
• The Transmit Overhead Data Input Interface block
• The Transmit HDLC Controller block.
• The Internal Overhead Data Generator.
Afterwards, this E3 data stream will be routed to the Transmit E3 LIU Interface block, for further processing.
Figure 107 presents a simple illustration of the Transmit E3 Framer block, along with the associated paths to
the other functional blocks within the chip.
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