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XRT79L71
PRELIMINARY
557
1-CHANNEL DS3/E3 CLEAR-CHANNEL FRAMERLIU COMBO - CC/HDLC ARCHITECTURE
REV. P2.0.0
NOTE: About
The answer to the very Is the Message Type ITU-T Path ID Decision Diamond of the flow-chart was obtained
during STEP 9 (see above).
STEP 11 - 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 255. 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.
6.3.5.2
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 E3, ITU-T G.832 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 "0" and that Bit 2 (Frame Format) is set to "1" as illustrated below.
FIGURE 256. FLOW-CHART DEPICTING AN APPROACH THAT ONE CAN USE 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