![](http://datasheet.mmic.net.cn/Exar-Corporation/XRT79L71IB-F_datasheet_100145/XRT79L71IB-F_574.png)
XRT79L71
PRELIMINARY
559
1-CHANNEL DS3/E3 CLEAR-CHANNEL FRAMERLIU COMBO - CC/HDLC ARCHITECTURE
REV. P2.0.0
STEP 5 - Check and verify that the Receive LAPD Controller is receiving the Flag Sequence Octets
If the Receive LAPD Controller block is currently receiving the Flag Sequence octets within the incoming E3
data-stream, then it will assert Bit 0 (Flag Present) within the Receive E3 LAPD Status Register, as depicted
below.
STEP 6 - Enable the Receive LAPD Interrupt (Optional).
This step is optional.
However, if this step is executed, the XRT79L71 will generate an interrupt to the
Microprocessor anytime the Receive LAPD Controller block has completed its reception of a new PMDL
Message. The purpose of this interrupt is to notify the Microprocessor that the Receive LAPD Message buffer
contains a newly received LAPD/PMDL Message that needs to be read.
The procedure for enabling the Receive LAPD Interrupt is actually a three-step process.
STEP 6a - Enable the DS3/E3 Framer block interrupts - At the Operational Block Level.
This step is accomplished by setting Bit 2 (DS3/E3 Framer Block Interrupt Enable) to "1" as illustrated below.
This step enables the DS3/E3 Framer block for interrupt generation at the Operational Block Level.
STEP 6b - Enable the Receive DS3/E3 Framer block Interrupts - At the Block Level.
This step is accomplished by setting Bit 7 (Receive DS3/E3 Framer Block Interrupt Enable), within the Framer
Block Interrupt Enable Register, to "1", as illustrated below.
Receive E3 LAPD Control Register - G.832 (Address = 0x1118)
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
RxLAPD Any
Unused
Receive
LAPD
from NR
Byte
Receive
LAPD
Enable
Receive
LAPD
Interrupt
Enable
Receive
LAPD
Interrupt
Status
R/W
R/O
R/W
RUR
0
X
1
0
Receive E3 LAPD Status Register (Address = 0x1119)
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
Unused
RxABORT
RxLAPDType[1:0]
RxCRType
RxFCSError
End of
Message
Flag Present
R/O
0
1
Operation Block Interrupt Enable Register - Byte 1 (Address = 0x0116)
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
Unused
DS3/E3
LIU/JA Block
Interrupt
Enable
DS3/E3
Framer
Block Inter-
rupt Enable
Unused
R/O
R/W
R/O
0
1
0