![](http://datasheet.mmic.net.cn/Exar-Corporation/XRT79L71IB-F_datasheet_100145/XRT79L71IB-F_222.png)
XRT79L71
PRELIMINARY
207
1-CHANNEL DS3/E3 CLEAR-CHANNEL FRAMERLIU COMBO - CC/HDLC ARCHITECTURE
REV. P2.0.0
The user can select between these two options by writing the appropriate value into Bit 0 (M-Sync Algo) within
the Receive DS3 Configuration and Status Register as depicted below.
The following table relates the contents of this Bit Field to the M-Bit Error criteria for Declaration of the OOF
defect condition for the M-bits.
THE DS3 OOF DEFECT DECLARATION CRITERIA FOR P-BIT ERRORS (OPTIONAL)
As mentioned earlier, the XRT79L71 offers the Framing with Valid P-Bits option, which configures the Receive
DS3 Framer block to verify correct P-bits prior to transitioning into the In-Frame state.
This particular
configuration setting also effects the OOF Defect Declaration criteria. More specifically, this same setting will
configure the Receive DS3 Framer block to also declare the OOF Defect Condition if a P-bit error is detected in
2 of the last 5 M-frames.
Whenever the Receive DS3 Framer block declares the OOF defect condition after being in the In-Frame State
the following will happen.
It will transition back into the F-Bit Search state within the Frame Acquisition/Maintenance Algorithm
Bit 4 (RxOOF Defect Declared) within the Receive DS3 Configuration and Status Register will be set to "1"
as depicted below.
The Receive DS3 Framer block will also issue a Change in the OOF Defect Condition interrupt request,
anytime there is a change in the OOF defect condition. The Receive DS3/E3 Framer block will indicate that
it is generating this interrupt by doing all of the following.
Receive DS3 Configuration and Status Register (Address = 0x1110)
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
RxAIS
Defect
Declared
RxLOS
Defect
Declared
RxIdle
Condition
Declared
RxOOF
Defect
Declared
Unused
Framing with
Valid P-Bits
F-Sync Algo
M-Sync Algo
R/O
R/W
0
1
0
1
0
TABLE 29: THE RELATIONSHIP BETWEEN THE CONTENTS OF BIT 0 (M-SYNC ALGO) WITHIN THE RECEIVE DS3
CONFIGURATION AND STATUS REGISTER, AND THE RESULTING M-BIT OOF DECLARATION CRITERIA FOR THE
RECEIVE DS3 FRAMER BLOCK
MSYNC ALGO
OOF DECLARATION CRITERIA
0
M-Bit Errors do not result in the declaration of the OOF defect condition.
1
The LOF/OOF defect condition will be declared if M-bit errors are detected within any 3 out of 4 consec-
utive DS3 frames.
Receive DS3 Configuration and Status Register (Address = 0x1110)
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
RxAIS
Defect
Declared
RxLOS
Defect
Declared
RxIdle
Condition
Declared
RxOOF
Defect
Declared
Unused
Framing with
Valid P-Bits
F-Sync Algo
M-Sync Algo
R/O
R/W
0
1
0
1
0