![](http://datasheet.mmic.net.cn/Exar-Corporation/XRT79L71IB-F_datasheet_100145/XRT79L71IB-F_247.png)
PRELIMINARY
XRT79L71
232
REV. P2.0.0
1-CHANNEL DS3/E3 CLEAR-CHANNEL FRAMERLIU COMBO - CC/HDLC ARCHITECTURE
NOTE: About
The answer to Is Message Type ITU-T Path? Decision Diamond within the flow-chart was obtained during STEP 8
(see above).
STEP 10 - Remove Header and FCS Bytes from this newly received and read out PMDL/LAPD Message
As mentioned above, the byte of the data, residing within the Receive LAPD Message buffer, will be as is
presented within Figure 98. Therefore, if the user is only interested in processing the Information Payload
portion of this LAPD/PMDL Message, then the user must remove these additional bytes from this block of data,
before further processing.
4.3.3.2
Receiving Non-Standard Variable Length (e.g., up to 82 bytes) LAPD Messages)
The user can (1) enable the Receive LAPD Controller, and (2) read out a non-Standard incoming PMDL/LAPD
message by executing the following steps.
STEP 1 - Make sure that the XRT79L71 has been configured to operate in the C-bit Parity Framing
Format.
This is accomplished by reading out the contents of the Frame Operating Mode Register (Address = 0x1100)
and verifying that Bit 6 (DS3/E3*) is set to "1" and that Bit 2 (Frame Format) is set to "0" as illustrated below.
FIGURE 98. FLOW-CHART DEPICTING AN APPROACH THAT CAN BE USED FOR READING OUT THE CONTENTS OF A
NEWLY RECEIVED
LAPD/PMDL MESSAGE FROM THE RECEIVE LAPD MESSAGE BUFFER
START
Set Init_Addr = 0x80
Set k = 0
Set Init_Addr = 0x80
Set k = 0
Write “Init_Addr” into Address Location 0x11C0
Read “Message_Byte[k]” from Address Location 0x11C1
Is
Message Type
ITU-T Path
ID?
Is
Message Type
ITU-T Path
ID?
Is k == 81?
Is k == 75?
k += 1
END
YES
NO
YES
NO
Init_Addr += 1