
XRT7245
DS3 UNI FOR ATM
á
PRELIMINARY
REV. 1.03
226
The Receive DS3 Framer will generate a “Change
in LOS Status” interrupt request. (
Note:
The
Receive DS3 Framer will also declare an “OOF”
condition and perform all of the “notification proce-
dures” as described in Section 7.1.2.2.2).
The Receive DS3 Framer will negate the “LOS” con-
dition when at least 60 out of 180 consecutive re-
ceived bits are “1”.
Note:
The Receive DS3 Framer will also generate the
“Change in LOS Condition” interrupt, when it negates the
LOS Condition.
The UNI chip allows the user to change the “LOS
Declaration criteria” such that an LOS condition is
declared only if the RLOS input pin (from the XRT7295
DS3 Line Receiver IC) is asserted. The “internally-
generated” LOS criteria of “180 consecutive 0s” will
be disabled. The user can accomplish this by writing
a “1” to bit 3 of the Rx DS3 Configuration and Status
Register, as depicted below.
Note:
For more information on the RLOS input pin, please
see Section 5.0.
7.1.2.3.2
The Receive DS3 Framer will identify and declare an
“AIS” condition if it detects all of the following condi-
tions in the incoming DS3 Data Stream:
Valid M-bits, F-bits and P-bits
All C-bits are zeros.
X-bits are set to “1”
The Payload portion of the DS3 Frame exhibits a
repeating “1010...” pattern
Alarm Indication Signal (AIS)
The Receive DS3 Framer contains, within its circuitry,
an Up/Down Counter that supports the “assertion”
and “negation” of the AIS condition. The counter
begins with the value of 00h upon power up or reset.
The counter is then incremented anytime the Receive
DS3 Framer detects an “AIS Type” M-frame. This
counter is then decremented, or kept at “zero” value,
when the Receive DS3 Framer detects a “non-AIS”
type M-frame. The Receive DS3 Framer will declare
an “AIS Condition” if this counter reaches the value of
63 M-frames or greater. Explained another way, the
AIS condition is declared if the number of AIS-type
M-frames is detected, such that it meets the following
conditions:
N
AIS
- N
VALID
63
where N
AIS
= the number of M-frames containing the
AIS pattern.
N
VALID
= the number of M-frames not containing the
AIS pattern
If at anytime, the contents of this Up/Down counter
exceeds 63 M-frames, then the Rx DS3 Framer will:
Assert the RxAIS output pin.
Set Bit 7 of the Rx DS3 Configuration and Status
Register, as depicted below.
Generate a “Change in AIS Status” Interrupt
Request to the local μP/μC.
The Receive DS3 Framer will negate the “AIS” condi-
tion when the following expression is true.
N
AIS
- N
VALID
μ 0.
In other words, once the Receive DS3 Framer has
detected a sufficient number of normal (or “Non-AIS”)
M-frames, such that this “Up/Down” counter reaches
“zero”, then the Receive DS3 Framer will negate the
“AIS Condition” indicators. The Receive DS3 Framer
will inform the local μC/μP of this negation of the “AIS
Status” by generating a “Change in AIS Status”
interrupt.
Rx DS3 Configuration and Status Register, (Address = 0Eh)
B
IT
7
B
IT
6
B
IT
5
B
IT
4
B
IT
3
B
IT
2
B
IT
1
B
IT
0
Rx AIS
Rx LOS
Rx Idle
Rx OOF
Int LOS Disable
Framing on Parity
F-Sync Algo M-Sync Algo
RO
RO
RO
RO
R/W
R/W
R/W
R/W
Rx DS3 Configuration and Status Register, (Address = 0Eh)
B
IT
7
B
IT
6
B
IT
5
B
IT
4
B
IT
3
B
IT
2
B
IT
1
B
IT
0
Rx AIS
Rx LOS
Rx Idle
Rx OOF
Int LOS Disable
Framing on Parity
F-Sync Algo
M-Sync Algo
1
X
X
X
X
X
X
X