![](http://datasheet.mmic.net.cn/Exar-Corporation/XRT79L71IB-F_datasheet_100145/XRT79L71IB-F_229.png)
PRELIMINARY
XRT79L71
214
REV. P2.0.0
1-CHANNEL DS3/E3 CLEAR-CHANNEL FRAMERLIU COMBO - CC/HDLC ARCHITECTURE
Clearing the AIS Defect Condition
The Receive DS3 Framer block will clear the AIS defect condition when the following expression is true.
NAIS - NVALID
0.
In other words, once the Receive DS3 Framer block 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 block will clear the AIS
Defect Condition.
The Receive DS3 Framer block will indicate that it is clearing the AIS defect by:
Setting Bit 7 (AIS Defect Declared) within the Receive DS3 Configuration and Status Register to "0", as
depicted below.
The Receive DS3 Framer block will also generate the Change in AIS Defect Condition interrupt, by asserting
the Interrupt Output pin (e.g., by pulling it "Low") and setting Bit 5 (Change of AIS Defect Condition Interrupt
Status), within the Receive DS3 Interrupt Status Register to "1" as illustrated below.
4.3.2.5
DECLARING AND CLEARING THE DS3 IDLE PATTERN
The Receive DS3/E3 Framer block has the responsibility for declaring and clearing the DS3 Idle condition
indicator, as described below.
4.3.2.5.1
Declaring the Idle Condition
The Receive DS3 Framer block will identify and declare an Idle Condition if it receives a sufficient number of
M-Frames within the DS3 data stream that meets all of the following conditions.
Valid M-bits, F-bits, and P-bits
The 3 CP-bits (in F-Frame #3) are zeros.
The X-bits are set to "1"
The payload portion of the DS3 Frame exhibits a repeating "1100..." pattern.
The Receive DS3 Framer block contains, within its circuitry, an Up/Down Counter that supports the assertion
and clearance of the Idle Condition. The counter begins with the value of 0x00 upon power up or reset. The
counter is incremented anytime the Receive DS3 Framer block detects an Idle-type M-frame. The counter is
Receive DS3 Configuration and Status Register (Address = 0x1110)
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
AISDefect
Declared
LOS Defect
Declared
Idle Condi-
tion Detected
OOF Defect
Declared
Unused
Framing with
Valid P-Bits
F-SyncAlgo
M-SyncAlgo
R/O
R/W
0
Receive DS3 Interrupt Status Register (Address = 0x1113)
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
Detection of
CP Bit Error
Interrupt
Status
Change of
LOS Defect
Condition
Interrupt
Status
Change of
AIS Defect
Condition
Interrupt
Status
Change of
Idle Condi-
tion Inter-
rupt
Status
Change of
FERF Defect
Condition
Interrupt
Status
Change of
AIC State
Interrupt
Status
Change of
OOF Defect
Condition
Interrupt
Status
Detection of
P-Bit Error
Interrupt
Status
RUR
0
1
0