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PRELIMINARY
XRT79L71
398
REV. P2.0.0
1-CHANNEL DS3/E3 CLEAR-CHANNEL FRAMERLIU COMBO - CC/HDLC ARCHITECTURE
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 8 - 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.
Table 47 indicates that if the value within the "RxLAPDType[1:0]" bit-fields are set to "[1, 1]", then the size of
total message residing within the Receive LAPD Message Buffer is 88 bytes, and that the size of the
Information Payload (within these 88 bytes of data) is 82 bytes. Likewise, this table also indicates that if the
value within the "RxLAPDType[1:0]" bit-fields are set to some value other than "[1, 1]", then the size of the total
message residing within the Receive LAPD Message Buffer is 82 bytes, and that the size of the Information
Payload (within these 82 bytes of data) is 76 bytes.
The Relationship between the Total LAPD/PMDL Message Size and Information Payload Size
The Relationship between the size of the Total (or complete) LAPD/PMDL Message, and the size of the
Information Payload, is best explained by presenting (again) the byte-format of the LAPD Message below in
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
RxFC
SError
End of
Message
Flag
Present
R/O
0
X
0
1
0
TABLE 47: THE RELATIONSHIP BETWEEN THE CONTENTS WITHIN BITS 4 AND 5 (RXLAPDTYPE[1:0]) AND THE TYPE
OF
LAPD/PMDL MESSAGE RESIDING WITHIN THE RECEIVE LAPD MESSAGE BUFFER
RXLAPDTYPE[1:0]
TYPE OF LAPD/PMDL MESSAGE RESIDING IN THE
RECEIVE LAPD MESSAGE BUFFER
SIZE OF MESSAGE RESIDING WITHIN THE
RECEIVE LAPD MESSAGE
BUFFER(INFORMATION PAYLOAD/TOTAL
MESSAGE SIZE)
00
CL Path Identification Message
76 Bytes/82 Bytes
01
Idle Signal Identification
76 Bytes/82 Bytes
10
Test Signal Identification
76 Bytes/82 Bytes
11
ITU-T Path Identification
82 Bytes/88 Bytes