XRT74L73 Datasheet, PDF (375/488 Pages) Exar Corporation – 3 CHANNEL, ATM UNI/PPP DS3/E3 FRAMING CONTROLLER

PRELIMINARY
XRT74L73
3 CHANNEL, ATM UNI/PPP DS3/E3 FRAMING CONTROLLER
REV. P1.0.1
• If the XRT74L73 Framer IC detects 2 consecutive
E3 frames that each contain 8 or more “0’s”.
Enabling and Disabling the Change in Receive
AIS Condition Interrupt
The user can enable or disable the Change in Re-
ceive LOS Condition Interrupt, by writing the appro-
priate value into Bit 0 (AIS Interrupt Enable), within
the RxE3 Interrupt Enable Register - 1, as indicated
below.
RXE3 INTERRUPT ENABLE REGISTER - 1 (ADDRESS = 0X12)
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
Not Used
COFA
Interrupt
Enable
OOF
Interrupt
Enable
RO
RO
RO
R/W
R/W
0
0
0
0
0
BIT 2
LOF
Interrupt
Enable
R/W
0
BIT 1
LOS
Interrupt
Enable
R/W
X
BIT 0
AIS
Interrupt
Enable
R/W
0
Setting this bit-field to “1” enables this interrupt. Con-
versely, setting this bit-field to “0” disables this inter-
rupt.
Servicing the Change in Receive AIS Condition
Interrupt
Whenever the XRT74L73 Framer IC detects this in-
terrupt, it will do all of the following.
• It will assert the Interrupt Request output pin (INT),
by driving it “Low”.
• It will set Bit 0 (AIS Interrupt Status), within the Rx
E3 Interrupt Status Register - 1 to “1”, as indicated
below.
Whenever the user’s system encounters the Change
in Receive AIS Condition Interrupt, then it should do
the following.
1. It should determine the current state of the AIS
condition. Recall, that this interrupt can be gen-
erated, whenever the XRT74L73 Framer IC
declares or clears the AIS defect. Hence, the
user can determine the current state of the AIS
defect by reading the state of Bit 3 (RxAIS) within
the Rx E3 Configuration and Status Register - 2,
as illustrated below.
RXE3 CONFIGURATION & STATUS REGISTER - 2 (ADDRESS = 0X11)
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
RxLOF
Algo
RxLOF
RxOOF
RxLOS
RxAIS
Not Used
RxFERF
R/W
RO
RO
RO
RO
RO
RO
RO
0
1
1
0
0
1
1
1
If the AIS Condition is TRUE
1. It should begin transmitting the FERF indication
to the Remote Terminal Equipment. Please see
Section 4.2.4.2.1.3 for instructions on how to
transmit a FERF condition.
If the AIS Condition is FALSE
2. It should cease transmitting the FERF indication
to the Remote Terminal Equipment. Please see
Section 4.2.4.2.1.3 for instructions on how to con-
trol the state of the “A” bit-field, within each out-
bound E3 frame.
5.3.6.2.5 The Change of Framing Alignment
Interrupt
If the Change of Framing Alignment Interrupt is en-
abled then the XRT74L73 Framer IC will generate an
interrupt any time the Receive E3 Framer block de-
tects an abrupt change of framing alignment.
NOTE: This interrupt is typically accompanied with the
Change in Receive OOF Condition interrupt as well.
Conditions causing the XRT74L73 Framer IC to
generate this interrupt.
If the XRT74L73 Framer detects receives at least four
consecutive E3 frames, within its Framing Alignment
bytes in Error, then the XRT74L73 Framer IC will de-
clare an OOF condition. However, while the
XRT74L73 Framer IC is operating in the OOF condi-
376