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XRT79L71
PRELIMINARY
201
1-CHANNEL DS3/E3 CLEAR-CHANNEL FRAMERLIU COMBO - CC/HDLC ARCHITECTURE
REV. P2.0.0
In this mode, the Receive DS3 Framer block is trying to maintain frame synchronization with the incoming DS3
Frames.
The operation of the Receive DS3 Framer block, in both the Frame Acquisition and the Frame Maintenance
Modes will be discussed, in considerable detail below.
4.3.2.1
THE FRAME-ACQUISITION MODE
The operation of the Receive DS3 Framer block, while in the Frame Acquisition mode, is best understood by
reviewing the Receive DS3 Framer block's Frame Acquisition/Maintenance Algorithm state machine diagram,
Processing through the Frame Acquisition Modes
The Receive DS3 Framer block will be performing Frame Acquisition operation while it is operating in the
following states per the DS3 Frame Acquisition/Maintenance algorithm State Machine diagram, as depicted in
F-bit Search
M-bit Search
Parity Check (optional)
Once the Receive DS3 Framer block enters the In-Frame state (per Figure 91), then it will begin Frame
Maintenance operation. The Receive DS3 Framer block's operation in each of the Frame Acquisition states is
presented below.
The F-bit Search State
When the XRT79L71 is first powered up, or exits a Hardware RESET event the Receive DS3 Framer block will
be operating in the frame-acquisition mode. At this point, the very first thing that the Receive DS3 Framer
FIGURE 91. THE STATE MACHINE DIAGRAM FOR THE RECEIVE DS3 FRAMER BLOCK'S FRAME ACQUISITION/MAIN-
TENANCE
ALGORITHM
F-Bit Search
M-Bit Search
F-Bit Synch
Achieved
In-Frame
RxOOF pin
is Negated.
10 Consecutive F-bits
Correctly Received
Parity Check
(Only if Framing
on Parity is
Selected)
M-bits Correctly
Detected for 3
Consecutive M-Frames
(Framing on Parity is
Selected)
M-bits Correctly
Detected for 3
Consecutive M-Frames
(Framing on Parity is
Not Selected)
OOF Criteria
based upon values
for F-Sync Algo
and M-Sync Algo
Valid Parity
Parity Error in
2 out of 5 frames