![](http://datasheet.mmic.net.cn/Exar-Corporation/XRT79L71IB-F_datasheet_100145/XRT79L71IB-F_490.png)
XRT79L71
PRELIMINARY
475
1-CHANNEL DS3/E3 CLEAR-CHANNEL FRAMERLIU COMBO - CC/HDLC ARCHITECTURE
REV. P2.0.0
NOTES:
1.
For normal operation, it is imperative that the user also make sure that bit 4 (Reserved) and bit 7 (LAPD Any)
within this register are both set to "0".
2.
Once the user executes the above mentioned step, then the Transmit LAPD Controller will begin to transmit the
Idle (Flag) Sequence (e.g., a continuous, repeating string of octets, of the value 0x7E) via either the NR or GC
bytes within each outbound E3 frame.
STEP 4 - Configure the Transmit LAPD Controller to Auto-Retransmit (Optional)
In some applications, it may be desirable to configure the Transmit LAPD Controller to repeatedly transmit a
LAPD/PMDL Message at one-second intervals. To configure the Transmit LAPD Controller block to do this,
write a "1" into Bit 3 (Auto Retransmit) within the Transmit E3 LAPD Configuration Register. This action is
depicted below.
STEP 5 - Specify the type of LAPD Message to be transmitted.
At this stage it is necessary to specify the type of LAPD Message, which is to be transmitted. The Transmit
and Receive LAPD Controller blocks within the XRT79L71 are capable of supporting the following standard
types of LAPD Messages.
Test Signal
Idle Signal
CL Path Identification
ITU Path Identification
The ITU Path Identification type of PMDL Message consists of an 82-byte information payload. All of the
remaining standard types of PMDL/LAPD Messages contain 76 byte information payloads. To transmit an 82
byte message (e.g., the ITU Path Identification type of LAPD Message), set Bit 1 (Transmit LAPD Message
Length), within the Transmit E3 LAPD Configuration Register to "1". For all of the remaining types of LAPD
Messages which are 76 bytes in length, set Bit 1 (Transmit LAPD Message Length) to "0". This operation is
depicted below.
Transmit E3 LAPD Configuration Register (Address = 0x1133)
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
LAPD
Any
Unused
Auto
Retransmit
Unused
Transmit
LAPD
Message
Length
Transmit
LAPD
Enable
R/W
RO
R/O
R/W
R/O
R/W
0
X
1
Transmit E3 LAPD Configuration Register (Address = 0x1133)
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
LAPD
Any
Unused
Auto
Retransmit
Unused
Transmit
LAPD
Message
Length
Transmit
LAPD
Enable
R/W
RO
R/O
R/W
R/O
R/W
0
1
0
X
1