XRT72L13 Datasheet, PDF (305/370 Pages) Exar Corporation – M13 MULTIPLEXER/CLEAR CHANNEL DS3 FRAMER IC

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PRELIMINARY
XRT72L13
M13 MULTIPLEXER/CLEAR CHANNEL DS3 FRAMER IC
REV. P1.0.6
Once the B3ZS (or AMI) encoded data has been de-
coded into a binary data-stream, the "Receive DS3
Framer" block will use portions of this data-stream in
order to synchronize itself to the "remote terminal
equipment". At any given time, the "Receive DS3
Framer" block will be operating in one of two modes.
• The Frame Acquisition Mode: In this mode, the
"Receive DS3 Framer" block is trying to acquire
synchronization with the incoming DS3 frames, or
• The Frame Maintenance Mode: In this mode, the
"Receive DS3 Framer" block is trying to maintain
frame synchronization with the incoming DS3
Frames.
Figure 100 presents a State Machine diagram that
depicts the "Receive DS3 Framer" block's "DS3
Frame Acquisition/Maintenance" Algorithm.
FIGURE 100. THE STATE MACHINE DIAGRAM FOR THE "RECEIVE DS3 FRAMER" BLOCK'S "FRAME ACQUISITION/
MAINTENANCE" 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 Ac-
quisition/Maintenance" algorithm State Machine dia-
gram, as depicted in Figure 100 .)
• 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 100 ), 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 in-
coming 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 Acquisi-
tion/Maintenance" algorithm state machine diagram
(see Figure 100 ). Recall from the discussion in Sec-
293