XRT74L73 Datasheet, PDF (239/488 Pages) Exar Corporation – 3 CHANNEL, ATM UNI/PPP DS3/E3 FRAMING CONTROLLER

PRELIMINARY
XRT74L73
3 CHANNEL, ATM UNI/PPP DS3/E3 FRAMING CONTROLLER
REV. P1.0.1
frame synchronization with the incoming DS3
Frames.
Figure 88 presents a State Machine diagram that de-
picts the Receive DS3 Framer block’s DS3 Frame Ac-
quisition/Maintenance Algorithm.
FIGURE 88. THE STATE MACHINE DIAGRAM FOR THE RECEIVE DS3 FRAMER BLOCK'S FRAME ACQUISITION/MAIN-
TENANCE ALGORITHM
F-Bit Search
OOF Criteria
based upon values
for F-Sync Algo
and M-Sync Algo
10 Consecutive F-bits
Correctly Received
M-Bit Search
F-Bit Synch
Achieved
M-bits Correctly
Detected for 3
Consecutive M-Frames
(Framing on Parity is
Not Selected)
Parity Error in
2 out of 5 frames
M-bits Correctly
Detected for 3
Consecutive M-Frames
(Framing on Parity is
Selected)
In-Frame
RxOOF pin
is Negated.
Valid Parity
Parity Check
(Only if Framing
on Parity is
Selected)
4.3.2.1 Frame Acquisition Mode Operation
The Receive DS3 Framer block will be performing
Frame Acquisition operation while it is operating in
any of the following states (per the DS3 Frame Acqui-
sition/Maintenance algorithm State Machine diagram,
as depicted in Figure 88 .)
• The F-bit Search state
• The M-bit Search state
• The P-Bit Check state (optional)
Once the Receive DS3 Framer block enters the In-
Frame state (per Figure 88 ), then it will begin Frame
Maintenance operation.
When the Receive DS3 Framer block is in the frame-
acquisition mode, it will begin to look for valid DS3
frames by first searching for the F-bits in the incoming
DS3 data stream. At this initial point the Receive
DS3 Framer block will be operating in the F-Bit
Search state within the DS3 Frame Acquisition/Main-
tenance algorithm state machine diagram (see
Figure 88 ). Recall from the discussion in Section 4.1,
that each DS3 F-frame consists of four (4) F-bits that
occur in a repeating 1001 pattern. The Receive DS3
Framer block will attempt to locate this F-bit pattern
by performing five (5) different searches in parallel.
The F-bit search has been declared successful if at
least 10 consecutive F-bits are detected. After the F-
bit match has been declared, the Receive DS3 Fram-
er block will then transition into the M-Bit Search state
within the DS3 Frame Acquisition/Maintenance algo-
rithm (per Figure 88 ). When the Receive DS3 Fram-
er block reaches this state, it will begin searching for
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