XRT72L50 Datasheet, PDF (183/471 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
Framer Operating Mode Register (Address = 0x00)
BIT 7
Local Loop-back
BIT 6
DS3/E3
R/W
R/W
0
1
BIT 5
Internal
LOS
Enable
R/W
1
BIT 4
RESET
R/W
0
BIT 3
Interrupt
Enable
Reset
R/W
1
BIT2
Frame
Format
R/W
X
BIT 1
BIT 0
TimRefSel[1:0]
R/W
R/W
X
X
This action will prevent the LAPD Transmitter from generating its own one-second interrupts.
2. Enable the One-Second Interrupt
This can be done by writing a "1" into Bit 0 of the Block Interrupt Enable Register, as depicted below.
Block Interrupt Enable Register (Address = 0x04)
BIT 7
RxDS3/E3
Interrupt
Enable
R/W
0
BIT 6
RO
0
BIT 5
BIT 4
Not Used
BIT 3
RO
RO
RO
0
0
0
BIT2
RO
0
BIT 1
TxDS3/E3
Interrupt
Enable
R/W
0
BIT 0
One Second
Interrupt
Enable
R/W
X
3. Write the new message into the Transmit LAPD Message buffer immediately after the occurrence of the
One-Second interrupt.
By timing the writes to the Transmit LAPD Message buffer to occur immediately after the occurrence of the
One-Second interrupt, the user avoids conflicting with the one-second transmissions of the LAPD Message,
and will transmit the correct messages to the remote LAPD Receiver.
4.2.4 The Transmit DS3 Framer Block
4.2.4.1 Brief Description of the Transmit DS3 Framer
The Transmit DS3 Framer block accepts data from any of the following three sources, and uses it to form the
DS3 data stream.
• The Transmit Payload Data Input block
• The Transmit Overhead Data Input block
• The Transmit HDLC Controller block
• The Internal Overhead Data Generator
The manner in how the Transmit DS3 Framer block handles data from each of these sources is described
below.
Handling of data from the Transmit Payload Data Input Interface
For DS3 applications, all data that is input to the Transmit Payload Data Input Interface will be inserted into the
payload bit positions within the outbound DS3 frames.
Handling of data from the Internal Overhead Bit Generator
By default, the Transmit DS3 Framer block will internally generate the overhead bits. However, if the Terminal
Equipment inserts its own values for the overhead bits (via the Transmit Overhead Data Input Interface) or, if
the user enables and employs the Transmit DS3 HDLC Controller block, then these internally generated
overhead bits will be overwritten.
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