XRT74L73
3 CHANNEL, ATM UNI/PPP DS3/E3 FRAMING CONTROLLER
REV. P1.0.1
PRELIMINARY
359
Table 78 presents the relationship between the con-
tents of RxLAPDType[1:0] and the type of message
received by the LAPD Receiver.
N
OTE
:
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
determine 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 150 presents a flow chart depict-
ing how the LAPD Receiver functions.
T
ABLE
78: T
HE
R
ELATIONSHIP
BETWEEN
THE
C
ONTENTS
OF
R
X
LAPDT
YPE
[1:0]
BIT
-
FIELDS
AND
THE
PMDL
M
ESSAGE
T
YPE
/S
IZE
R
X
LAPDT
YPE
[1:0]
PMDL M
ESSAGE
T
YPE
PMDL M
ESSAGE
S
IZE
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
B
IT
7
B
IT
6
B
IT
5
B
IT
4
B
IT
3
B
IT
2
B
IT
1
B
IT
0
Not Used
RxLAPD
Enable
RxLAPD
Interrupt Enable
RxLAPD
Interrupt Status
RO
RO
RO
RO
RO
R/W
R/W
RUR
0
0
0
0
0
0
0
1
RXE3 LAPD STATUS REGISTER (ADDRESS = 0X19)
B
IT
7
B
IT
6
B
IT
5
B
IT
4
B
IT
3
B
IT
2
B
IT
1
B
IT
0
Not Used
RxABORT
RxLAPDType[1:0]
RxCR
Type
RxFCS
Error
End of
Message
Flag
Present
RO
RO
RO
RO
RO
RO
RO
RO
0
0
0
0
0
0
1
0