XRT74L74
4 CHANNEL, ATM UNI/PPP DS3/E3 FRAMING CONTROLLER
ADVANCED CONFIDENTIAL
REV. P1.1.1
284
It will set Bit 6 (LOS Interrupt Status) within the
RxDS3 Interrupt Status register to “1”, as illustrated
below.
Whenever the user’s system encounters the Change
of LOS on Receive Interrupt, then it should do the fol-
lowing.
1.
It should determine the current state of the LOS
condition. Recall, that this interrupt can gener-
ated, whenever the XRT74L74 Framer declares
or clears the LOS defects. Hence, the current
state of the LOS defect can be determined by
reading the state of Bit 6 (RxLOS), within the
RxDS3 Configuration & Status Registers, as illus-
trated below.
If the LOS State is TRUE
1.
It should transmit a FERF (Far-End Receive Fail-
ure) to the Remote Terminal Equipment. The
XRT74L74 Framer IC automatically supports this
action via the FERF-upon-LOS feature.
2.
It should transmit the appropriate FEAC Message
(per Bellcore GR-499-CORE), to the Remote Ter-
minal, indicating that a Loss of Signal condition
has been declared.
If the LOS State is FALSE
1.
It should cease transmitting a FERF indicator to
the Remote Terminal Equipment. The XRT74L74
Framer IC automatically supports this action via
the FERF-upon-LOS feature.
2.
It should transmit the appropriate FEAC Message
(per Bellcore GR-499-CORE), to the Remote Ter-
minal Equipment, indicating that the Loss of Sig-
nal condition has been cleared.
5.3.6.2.2
The Change of State on Receive OOF
Interrupt
If the Change of State on Receive OOF (Out-of-
Frame) Interrupt is enabled, then the XRT74L74
Framer IC will generate an interrupt in response to ei-
ther of the following conditions.
1.
When the XRT74L74 Framer IC declares an OOF
(Out of Frame) condition, and
2.
When the XRT74L74 Framer IC clears the OOF
(Out of Frame) condition.
Conditions causing the XRT74L74 Framer IC to
declare an OOF condition
If the Receive DS3 Framer block (within the
XRT74L74 Framer IC) detects at least either 3 or 6
F-bit errors, in the last 16 F-bits.
Conditions causing the XRT74L74 Framer IC to
clear the OOF condition.
Whenever, the Receive DS3 Framer block transi-
tions from the M-Bit Search into the In-Frame state
(within the Frame Acquisition/Maintenance State
Machine Diagram).
Enabling and Disabling the Change of State on
Receive OOF Interrupt:
The Change of State on Receive OOF Interrupt can
be enabled or disabled by writing the appropriate val-
RXDS3 INTERRUPT STATUS REGISTER (ADDRESS = 0X13)
B
IT
7
B
IT
6
B
IT
5
B
IT
4
B
IT
3
B
IT
2
B
IT
1
B
IT
0
CP-Bit Error
Interrupt
Status
RUR
0
LOS
Interrupt
Status
RUR
1
AIS
Interrupt
Status
RUR
0
Idle Interrupt
Status
FERF
Interrupt
Status
RUR
0
AIC
Interrupt
Status
RUR
0
OOF
Interrupt
Status
RUR
0
P-Bit Error
Interrupt
Status
RUR
0
RUR
0
RXDS3 CONFIGURATION & STATUS REGISTER (ADDRESS = 0X10)
B
IT
7
B
IT
6
B
IT
5
B
IT
4
B
IT
3
B
IT
2
B
IT
1
B
IT
0
RxAIS
RxLOS
RxIdle
RxOOF
Reserved
Framing On
Parity
R/W
0
FSync
Algo
R/W
0
MSync
Algo
R/W
0
RO
0
RO
1
RO
0
RO
0
RO
0