XRT74L73 Datasheet, PDF (238/488 Pages) Exar Corporation – 3 CHANNEL, ATM UNI/PPP DS3/E3 FRAMING CONTROLLER

XRT74L73
3 CHANNEL, ATM UNI/PPP DS3/E3 FRAMING CONTROLLER
REV. P1.0.1
PRELIMINARY
FIGURE 86. WAVEFORM/TIMING RELATIONSHIP BETWEEN RXLINECLK, RXPOS AND RXNEG - WHEN RXPOS AND
RXNEG ARE TO BE SAMPLED ON THE FALLING EDGE OF RXLINECLK
RxLineClk
t40
t41
RxPOS
RxNEG
4.3.2 The Receive DS3 Framer Block
The Receive DS3 Framer block accepts decoded
DS3 data from the Receive DS3 LIU Interface block,
and routes data to the following destinations.
• The Receive Payload Data Output Interface Block
• The Receive Overhead Data Output Interface
Block.
• The Receive DS3 HDLC Controller Block
Figure 87 presents a simple illustration of the Re-
ceive DS3 Framer block along with the associated
paths to the other functional blocks within the Framer
chip.
FIGURE 87. A SIMPLE ILLUSTRATION OF THE RECEIVE DS3 FRAMER BLOCK AND THE ASSOCIATED PATHS TO THE
OTHER FUNCTIONAL BLOCKS
To Receive DS3 HDLC
Buffer
Receive Overhead Data
Output Interface
Receive Payload Data
Output Interface
RReecceeiviveeDDSS33FFrraammeerr
BBlolocckk
From Receive DS3
LIU Interface Block
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 syn-
chronization with the incoming DS3 frames, or
• The Frame Maintenance Mode: In this mode, the
Receive DS3 Framer block is trying to maintain
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