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XRT79L71
PRELIMINARY
555
1-CHANNEL DS3/E3 CLEAR-CHANNEL FRAMERLIU COMBO - CC/HDLC ARCHITECTURE
REV. P2.0.0
Table 69 presents the relationship between the contents within Bits 4 and 5 (RxLAPDType[1:0]) and the
corresponding LAPD Message that is residing within the Receive LAPD Message Buffer.
Table 69 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 LAPD/PMDL Message, and the size of the Information Payload,
is best explained by presenting the byte-format of the LAPD Message below in Figure 255.
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
1
0
TABLE 69: 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
FIGURE 255. LAPD MESSAGE FRAME FORMAT
FLAG SEQUENCE (8 BITS)
SAPI (6-bits)
C/R
EA
TEI (7 bits)
EA
Control (8-bits)
76 OR 82 OR ANY-SIZE BYTES OF INFORMATION (PAYLOAD)
FCS - MSB
FCS - LSB
Flag Sequence (8-bits)