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PRELIMINARY
XRT79L71
206
REV. P2.0.0
1-CHANNEL DS3/E3 CLEAR-CHANNEL FRAMERLIU COMBO - CC/HDLC ARCHITECTURE
small number of errors, the Receive DS3 Framer block will continue to declare itself being in the In-Frame
condition, and will continue to operate in the Frame Maintenance Mode. However, if the Receive DS3 Framer
block begins to detect a large number of certain types of errors within the incoming DS3 data-stream then it will
exit the In-Frame state and will then declare the OOF Defect condition. In short, the Receive DS3 Framer
block will declare the OOF defect condition when any one of the following events occur.
When 3 or 6 F-bits (depending upon user setting), within the last 16 received F-bits are incorrect.
When M-bit errors are detected within 3 out of four (4) consecutive incoming DS3 frames (optional)
When P-bit errors are detected within 2 out of five (5) consecutive incoming DS3 frames (optional).
Each of these events that can possibly cause the Receive DS3 Framer block to declare the OOF defect
condition will be discussed in some detail below. Additionally, any configuration options that permit the user to
select or modify the OOF Defect Declaration criteria will be discussed below.
THE DS3 OOF DEFECT DECLARATION CRITERIA FOR F-BIT ERRORS
While the Receive DS3 Framer block is operating in the Frame Maintenance mode, it will declare an Out-of-
Frame (OOF) defect condition anytime it determines that 3 or 6 F-bits (depending upon user selection) out of
16 consecutive F-bits are in error. The user makes this selection for the OOF Defect Declaration criteria by
writing the appropriate value into bit 1 (F-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 OOF Defect Declaration criteria for the F-bits.
NOTE: Once the Receive DS3 Framer block has declared the OOF Defect condition, it will transition back to the F-Bit
Search state within the DS3 Frame Acquisition/Maintenance algorithm (per
THE DS3 OOF DEFECT DECLARATION CRITERIA FOR M-BIT ERRORS
In addition to selecting the OOF Defect Declaration criteria for the F-bits, the user has the following two options
for configuring the OOF Defect Declaration criteria based upon M-bits.
1.
M-bit errors do not result in the declaration of the OOF/LOF defect condition, or
2.
The LOF/OOF defect condition will be declared if M-bit errors are detected within any three (3) out of four
(4) consecutive 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
TABLE 28: THE RELATIONSHIP BETWEEN THE CONTENTS OF BIT 1 (F-SYNC ALGO) WITHIN THE RECEIVE DS3
CONFIGURATION AND STATUS REGISTER, AND THE RESULTING F-BIT OOF DECLARATION CRITERIA FOR THE
RECEIVE DS3 FRAMER BLOCK
F-SYNC ALGO (BIT 1)
OOF DECLARATION CRITERIA
0
OOF is declared when 6 out of 16 consecutive F-bits are determined to be in error.
1
OOF is declared when 3 out of 16 consecutive F-bits are determined to be in error.