
á
XRT7250
DS3/E3 FRAMER IC
REV. 1.1.1
307
Table 62 presents the relationship between the con-
tents of RxLAPDType[1:0] and the type of message
received by the LAPD Receiver.
NOTE: Prior to reading in the PMDL Message from the
Receive LAPD Message buffer, the user is urged to read
the state of the RxLAPDType[1:0] bit-fields in order to deter-
mine the size of this message.
5. Inform the Local Microprocessor/External Cir-
cuitry of the receipt of the new LAPD Message
frame.
Finally, after the LAPD Receiver has received and
processed the newly received LAPD Message frame
(per steps 1 through 4, as described above), it will in-
form the local Microprocessor that a LAPD Message
frame has been received and is ready for user-sys-
tem handling. The LAPD Receiver will inform the Mi-
croprocessor/Microcontroller and the external circuit-
ry by:
Generating a LAPD Message Frame Received
interrupt to the Microprocessor. The purpose of
this interrupt is to let the Microprocessor know that
the Receive LAPD Message buffer contains a new
PMDL Message that needs to be read and pro-
cessed. When the LAPD Receiver generates this
interrupt, it will set bit 0 (RxLAPD Interrupt Status)
within the Rx E3 LAPD Control Register to “1” as
depicted below.
)
Setting Bit 1 (End of Message) within the Rx E3
LAPD Status Register, to “1” as depicted below.
In summary,
Figure 143 presents a flow chart depict-
ing how the LAPD Receiver functions.
TABLE 62: 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
Test Signal Identification
76 Bytes
01
Idle Signal Identification
76 Bytes
10
CL Path Identification
76 Bytes
11
ITU-T Path Identification
82 Bytes
RXE3 LAPD CONTROL REGISTER (ADDRESS = 0X18
BIT 7BIT 6BIT 5BIT 4BIT 3BIT 2BIT 1BIT 0
Not Used
RxLAPD
Enable
RxLAPD
Interrupt Enable
RxLAPD
Interrupt Status
RO
R/W
RUR
00000
0
1
RXE3 LAPD STATUS REGISTER (ADDRESS = 0X19)
BIT 7BIT 6BIT 5BIT 4BIT 3BIT 2BIT 1BIT 0
Not Used
RxABORT
RxLAPDType[1:0]
RxCR
Type
RxFCS
Error
End of
Message
Flag
Present
RO
0
0000
010