XRT72L50 Datasheet, PDF (394/471 Pages) Exar Corporation – SINGLE CHANNEL DS3/E3 FRAMER IC WITH HDLC CONTROLLER

XRT72L50
SINGLE CHANNEL DS3/E3 FRAMER WITH HDLC CONTROLLER
REV. 1.2.1
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problem, while writing the new message into the Transmit LAPD Message buffer, the user should do the
following.
1. Configure the Framer to automatically reset activated interrupts.
The user can do this by writing a “1” into Bit 3 within the Framer Operating Mode register (Address = 0x00), as
depicted below.
Framer Operating Mode Register (Address = 0x00)
BIT 7
Local Loop-back
BIT 6
DS3/E3*
R/W
R/W
0
0
BIT 5
Internal
LOS
Enable
R/W
1
BIT 4
RESET
BIT 3
Interrupt
Enable Reset
BIT 2
Frame Format
R/W
R/W
R/W
0
1
0
BIT 1
BIT 0
TimRefSel[1:0]
R/W
R/W
1
1
This action will prevent the LAPD Transmitter from generating its own One-Second interrupt (following each
transmission of the LAPD Message frame).
2. Enable the One-Second Interrupt
This can be done by writing a “1” into Bit 0 (One-Second Interrupt Enable) within 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
BIT 2
RO
0
BIT 1
TxDS3/E3
Interrupt
Enable
R/W
0
BIT 0
One-Second
Interrupt
Enable
R/W
1
3. Write the new message into the Transmit LAPD Message buffer immediately after the occurrence of the
One-Second Interrupt
By synchronizing 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 transmission of the LAPD Message
frame, and will transmit the correct (uncorrupted) PMDL Message to the Remote LAPD Receiver.
6.2.4 The Transmit E3 Framer Block
6.2.4.1 Brief Description of the Transmit E3 Framer
The Transmit E3 Framer block accepts data from any of the following four sources, and uses it to form the E3
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 E3 Framer block handles data from each of these sources is described below.
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.
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