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PRELIMINARY
XRT79L71
554
REV. P2.0.0
1-CHANNEL DS3/E3 CLEAR-CHANNEL FRAMERLIU COMBO - CC/HDLC ARCHITECTURE
This step is accomplished by setting Bit 1 (Receive LAPD Interrupt Enable), within the Receive DS3 LAPD
Control Register, as depicted below.
STEP 6 - Wait for the occurrence of the Receive LAPD Interrupt
STEP 7 - Service the Receive LAPD Interrupt
Receive LAPD Interrupt.
STEP 8 - Check and verify that there are no FCS (Frame Check Sequence) Errors within the LAPD/
PMDL Message that is residing within the Receive LAPD Message Buffer.
This can be accomplished by reading out and testing the state of Bit 2 (RxFCS Error) within the Receive E3
LAPD Status Register as depicted below.
If this bit-field is set to "0", then the Receive LAPD Controller block has received this particular LAPD Message
that is residing within the Receive LAPD Message Buffer in an un-erred manner (e.g., there are no FCS errors
within this particular LAPD message).
Conversely, if this bit-field is set to "1", then the Receive LAPD
Controller block has received this particular LAPD Message that is residing within the Receive LAPD Message
Buffer in an erred manner.
NOTE: The Receive LAPD Controller block will not generate any interrupt in response to it detecting any FCS Errors within
an incoming LAPD Message. The user is expected to validate each incoming LAPD Message, by testing the state
of the RxFCS Error bit-field, prior to processing a given message.
STEP 9 - Identify the Type and Size of Message that the Receive LAPD Controller has just received.
This can be accomplished by reading out the contents of Bits 4 and 5 (RxLAPDType[1:0]) within the Receive
E3 LAPD Status Register, as depicted below.
Receive E3 LAPD Control Register (Address = 0x1118)
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
RxLAPD
Any
Unused
Receive
LAPD
Enable
Receive
LAPD
Interrupt
Enable
Receive
LAPD
Interrupt
Status
R/W
R/O
R/W
RUR
0
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]
RxCR
Type
RxFCS
Error
End of
Message
Flag
Present
R/O
0
X
0
X
0