XRT72L50 Datasheet, PDF (206/471 Pages) Exar Corporation – SINGLE CHANNEL DS3/E3 FRAMER IC WITH HDLC CONTROLLER

XRT72L50
SINGLE CHANNEL DS3/E3 FRAMER WITH HDLC CONTROLLER
REV. 1.2.1
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• The Frame Maintenance Mode: In this mode, the Receive DS3 Framer block is trying to maintain frame
synchronization with the incoming DS3 Frames.
Figure 69 presents a State Machine diagram that depicts the Receive DS3 Framer block's DS3 Frame
Acquisition/Maintenance Algorithm.
FIGURE 69. 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 Acquisition/Maintenance algorithm State Machine diagram, as depicted in
Figure 69.)
• 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 69), 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/Maintenance algorithm state
machine diagram (see Figure 69). Each DS3 F-frame consists of four (4) F-bits that occur in a repeating 1001
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