XRT74L73 Datasheet, PDF (478/488 Pages) Exar Corporation – 3 CHANNEL, ATM UNI/PPP DS3/E3 FRAMING CONTROLLER

XRT74L73
3 CHANNEL, ATM UNI/PPP DS3/E3 FRAMING CONTROLLER
REV. P1.0.1
PRELIMINARY
1. When the XRT74L73 Framer IC declares an LOF
(Out of Frame) Condition, and
2. When the XRT74L73 Framer IC clears the LOF
condition.
Conditions causing the XRT74L73 Framer IC to
declare an LOF Condition.
• If the Receive E3 Framer block (within the
XRT74L73 Framer IC) detects Framing Byte errors,
within four consecutive incoming E3 frames and is
not able to transition back into the In-Frame state
within 1 or 3ms.
Conditions causing the XRT74L73 Framer IC to
clear the LOF Condition.
• If the Receive E3 Framer block transitions from the
OOF Condition state to the LOF Condition state
(see Figure 175).
• If the Receive E3 Framer block transitions back into
the In-Frame state.
Enabling and Disabling the Change in Receive
LOF Condition Interrupt
The user can enable or disable the Change in Re-
ceive LOF Condition Interrupt, by writing the appropri-
ate value into Bit 3 (LOF Interrupt Enable), within the
RxE3 Interrupt Enable Register - 1, as indicated be-
low.
RXE3 INTERRUPT ENABLE REGISTER - 1 (ADDRESS = 0X12)
BIT 7
RO
0
BIT 6
Not Used
RO
0
BIT 5
RO
0
BIT 4
COFA
Interrupt
Enable
R/W
0
BIT 3
OOF
Interrupt
Enable
R/W
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 LOF 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 6 (LOF Interrupt Status), within the Rx
E3 Interrupt Status Register - 1 to “1”, as indicated
below.
RXE3 CONFIGURATION & STATUS REGISTER 2 (ADDRESS = 0X11)
BIT 7
Rx LOF Algo
BIT 6
RxLOF
R/W
RO
X
X
BIT 5
RxOOF
RO
X
BIT 4
RxLOS
RO
X
BIT 3
RxAIS
RO
X
BIT 2
RxPld Unstab
RO
X
BIT 1
Rx
TMark
RO
X
BIT 0
RxFERF
RO
X
6.3.6.2.4 The Change of Framing Alignment
(COFA) 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-
tion, it will still rely on the old framing alignment for E3
payload data extraction, etc.
However, if the Receive E3 Framer had to change
alignment, in order to re-acquire frame synchroniza-
tion, then this interrupt will occur.
Enabling and Disabling the Change of Framing
Alignment Interrupt
The user can enable or disable the Change of Fram-
ing Alignment Interrupt by writing the appropriate val-
ue into Bit 4 (COFA Interrupt
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