![](http://datasheet.mmic.net.cn/Exar-Corporation/XRT79L71IB-F_datasheet_100145/XRT79L71IB-F_220.png)
XRT79L71
PRELIMINARY
205
1-CHANNEL DS3/E3 CLEAR-CHANNEL FRAMERLIU COMBO - CC/HDLC ARCHITECTURE
REV. P2.0.0
The Table 27 relates the contents of this bit field to the framing acquisition criteria.
The In-Frame State
If the Receive DS3 Framer block either declares the M-Bit Sync condition or successfully passes through the
Parity-Check state, then it will declare itself in the In-Frame condition, and will begin Frame Maintenance
operations. The Receive DS3 Framer block will then indicate that it has transitioned from the OOF condition
into the In-Frame condition by doing the following.
Generate a Change in OOF Defect Condition interrupt to the C/P.
Set Bit 4 (Rx OOF Defect Declared) within the Receive DS3 Configuration and Status Register to "0" as
depicted below.
Once the Receive DS3 Framer block is in the In-Frame condition, normal data recovery and processing of the
DS3 data stream begins. The maximum average reframing time of the Receive DS3/E3 Framer block is less
than 1.5 ms.
4.3.2.2
THE FRAME-MAINTENANCE MODE - THE OOF/LOF DEFECT DECLARATION CRITERIA
When the Receive DS3 Framer block is operating in the In-Frame state (per Figure 91), it will then begin to
perform Frame Maintenance operations, where it will continue to verify that the F- and M-bits are present, at
their proper locations. In general, as long as the F- and M-bits are present and at their proper locations with a
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 27: THE RELATIONSHIP BETWEEN THE CONTENTS OF BIT 2 (FRAMING WITH VALID P-BITS) WITHIN THE RX DS3
CONFIGURATION AND STATUS REGISTER, AND THE RESULTING FRAMING ACQUISITION CRITERIA
FRAMING WITH VALID
P-BITS (BIT 2)
FRAMING ACQUISITION CRITERIA
0
The In-frame is declared after F-bit synchronization (10 or 16 F-bit matches) followed by M-bit syn-
chronization (M-bit matches for 3 DS3 M-frames)
NOTE: In this case, the P-bits are not checked as part of the In-Frame declaration criteria.
1
The In-frame condition is declared after F-bit synchronization, followed by M-bit synchronization,
with valid parity over the frames. Also, the occurrence of parity or P-bit errors in 2 or more out of 5
frames starts a frame search
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