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XRT79L71
PRELIMINARY
373
1-CHANNEL DS3/E3 CLEAR-CHANNEL FRAMERLIU COMBO - CC/HDLC ARCHITECTURE
REV. P2.0.0
5.3.2.1
THE FRAME-ACQUISITION MODES
The operation of the Receive E3 Framer block, while in the "Frame Acquisition" mode is best understood by
reviewing the "Receive E3 Framer Block's Frame Acquisition/Maintenance Algorithm" state machine diagram,
Processing through the Frame Acquisition Modes
The Receive E3 Framer block will be performing "Frame Acquisition" operation while it is operating in the
following states (per the "E3, ITU-T G.751 Frame Acquisition/Maintenance" algorithm State Machine diagram,
FAS Pattern Search
FAS Pattern Verification
OOF State
LOF State
Once the Receive E3 Framer block enters the "In-Frame" state (per Figure 174), then it will begin "Frame
Maintenance" Operation. The Receive E3 Framer block's operation in each of the "Frame Acquisition" states
is presented below.
The "FAS Pattern Search" State
When the XRT79L71 is first powered up, or a "Hardware RESET" event occurs, the Receive E3 Framer block
will be operating in the "Frame Acquisition" Mode. At this point, the very first thing that the Receive E3 Framer
block will do is to begin to look for valid E3 frames (within the incoming E3 data-stream) by first searching for
the FAS pattern. At this "initial point" the Receive E3 Framer block will be operating in the "FAS Pattern
Search" state within the "E3 Frame Acquisition/Maintenance" Algorithm state machine diagram. In order to
FIGURE 174. THE RECEIVE E3 FRAMER BLOCK'S FRAME ACQUISITION/MAINTENANCE ALGORITHM - E3, ITU-T
G.751 APPLICATIONS
FAS
Pattern
Search
FAS
Pattern
Search
LOF
State
LOF
State
OOF
State
OOF
State
In Frame
State
In Frame
State
FAS
Pattern
Verification
FAS
Pattern
Verification
FAS Pattern is
detected Once
FAS Pattern is
NOT Detected
FAS Patten is verified
Three consecutive times
4 Consecutive
Invalid Frames
3 Consecutive
Valid Frames
8 or 24 frame periods of
Operating in the “OOF State”
(User Selectable)
Frame Maintenance
Mode