![](http://datasheet.mmic.net.cn/Exar-Corporation/XRT79L71IB-F_datasheet_100145/XRT79L71IB-F_331.png)
PRELIMINARY
XRT79L71
316
REV. P2.0.0
1-CHANNEL DS3/E3 CLEAR-CHANNEL FRAMERLIU COMBO - CC/HDLC ARCHITECTURE
STEP 5 - 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
PMDL Message at one-second intervals. To configure the Transmit LAPD Controller to do this, write a "1" into
Bit 3 (Auto-Retransmit) within the Transmit E3 LAPD Configuration register. This operation is depicted below.
STEP 6 - Specify the size of the outbound LAPD Message
This is accomplished by writing the size of the information payload (in terms of number of bytes) into the
Transmit LAPD Byte Count Register, as depicted below.
STEP 7 - Load the Transmit LAPD Message Buffer
The next step is to load into the contents of the outbound LAPD/PMDL Message into the Transmit LAPD
Message Buffer. Whenever the user wishes to load in the contents o the outbound PMDL/LAPD Message into
the Transmit LAPD Message buffer, then the user MUST employ an Indirect Addressing scheme that will be
presented below.
In order to begin the process of loading in the contents of the outbound PMDL Message, the user must be
aware of the following important Address Locations, within the XRT79L71 Address space.
1.
The LAPD Message Buffer - Indirect Address Register - Address = 0x11C0
2.
The LAPD Message Buffer - Indirect Data Register - Address = 0x11C1
Transmit E3 LAPD Configuration Register (Address = 0x1133)
IT 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
1
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
1
0
1
0
X
1
Transmit LAPD Byte Count Register (Address = 0x1183)
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
TxLAPD_MESSAGE_SIZE[7:0]
R/W
X