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XRT72L52
323
REV. 1.0.3
TWO CHANNEL DS3/E3 FRAMER IC WITH HDLC CONTROLLER
NOTE: The LAPD Receiver will extract and write the PMDL Message into the Receive LAPD Message buffer independent
of the results of FCS Verification. Hence, the user is urged to validate each PMDL Message that is read in from the
Receive LAPD Message buffer, by first checking the state of this bit-field.
3. Check and Report the State of the C/R Bit-field
After receiving the LAPD Message frame, the LAPD Receiver will check the state of the C/R bit-field, within
octet # 2 of the LAPD Message frame header and will reflect this value in Bit 3 (Rx CR Type) within the Rx E3
LAPD Status Register, as depicted below.
When this bit-field is “0”, it means that this LAPD Message frame is originating from a customer installation.
When this bit-field is “1”, it means that this LAPD Message frame is originating from a network terminal.
4. Identify the Type of LAPD Message Frame/PMDL Message
Next, the LAPD Receiver will check the value of the first octet within the PMDL information payload field, of the
LAPD Message frame. When operating the LAPD Transmitter, the user is required to write in a byte of a
specific value at address ox8A within the Transmit LAPD Message buffer. The value of this byte corresponds
to the type of LAPD Message frame/PMDL Message that is to be transmitted to the Remote LAPD Receiver.
This Message-Type Identification octet is transported to the Remote LAPD Receiver, along with the rest of the
LAPD frame. From this Message Type Identification octet, the LAPD Receiver will know the type of size of the
newly received PMDL Message.
The LAPD Receiver will then reflect this information in Bits 4 and 5
(RxLAPDType[1:0]) within the Rx E3 LAPD Status Register, as depicted below.
Table 68 presents the relationship between the contents of RxLAPDType[1:0] and the type of message
received by the LAPD Receiver.
RXE3 LAPD STATUS REGISTER (ADDRESS = 0X19)
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
Not Used
RxABORT
RxLAPDType[1:0]
RxCR
Type
RxFCS
Error
End of
Message
Flag
Present
RO
0
1
0
RXE3 LAPD STATUS REGISTER (ADDRESS = 0X19)
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
Not Used
RxABORT
RxLAPDType[1:0]
RxCR
Type
RxFCS
Error
End of
Message
Flag
Present
RO
0
TABLE 68: THE RELATIONSHIP BETWEEN THE CONTENTS OF RXLAPDTYPE[1:0] BIT-FIELDS AND THE PMDL
MESSAGE TYPE/SIZE
RXLAPDTYPE[1:0]
PMDL MESSAGE TYPE
PMDL MESSAGE SIZE
00
CL Path Identification
76 Bytes
01
Idle Signal Identification
76 Bytes
10
Test Signal Identification
76 Bytes
11
ITU-T Path Identification
82 Bytes