XRT79L71
PRELIMINARY
235
1-CHANNEL DS3/E3 CLEAR-CHANNEL FRAMERLIU COMBO - CC/HDLC ARCHITECTURE
REV. P2.0.0
STEP 6 - Wait for the occurrence of the Receive LAPD Interrupt
STEP 7 - Service the 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 DS3
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 - Determine the Size of the Message that the Receive LAPD Controller has just received.
This can be accomplished by reading out the contents of the Receive LAPD Byte Count Register, as depicted
below.
NOTES:
1.
The Receive LAPD Byte Count Register will have the size of the newly received LAPD/PMDL Message, in terms
of bytes.
Receive DS3 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 DS3 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
Receive LAPD Byte Count Register (Address = 0x1184)
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
RxLAPD_MESSAGE_SIZE[7:0]
R/O
0