XRT72L50 Datasheet, PDF (413/471 Pages) Exar Corporation – SINGLE CHANNEL DS3/E3 FRAMER IC WITH HDLC CONTROLLER

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XRT72L50
SINGLE CHANNEL DS3/E3 FRAMER WITH HDLC CONTROLLER
REV. 1.2.1
6.3.2 The Receive E3 Framer Block
The Receive E3 Framer block accepts decoded E3 data from the Receive E3 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 E3 HDLC Controller Block
Figure 181 presents a simple illustration of the Receive E3 Framer block, along with the associated paths to
the other functional blocks within the Framer chip.
FIGURE 181. THE RECEIVE E3 FRAMER BLOCK AND THE ASSOCIATED PATHS TO OTHER FUNCTIONAL BLOCKS
To Receive E3 HDLC
Buffer
Receive Overhead
Data Output Interface
Receive Payload
Data Output Interface
Receive
E3 Framer
Block
From Receive E3
LIU Interface Block
Once the HDB3 (or AMI) encoded data has been decoded into a binary data-stream, the Receive E3 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 E3 Framer block will be operating in one of two modes.
• The Frame Acquisition Mode: In this mode, the Receive E3 Framer block is trying to acquire
synchronization with the incoming E3 frame, or
• The Frame Maintenance Mode: In this mode, the Receive E3 Framer block is trying to maintain frame
synchronization with the incoming E3 Frames.
Figure 182 presents a State Machine diagram that depicts the Receive E3 Framer block's E3/ITU-T G.832
Frame Acquisition/Maintenance Algorithm.
6.3.2.1 The Framing Acquisition Mode
The Receive E3 Framer block is considered to be operating in the Frame Acquisition Mode, if it is operating in
any one of the following states within the E3 Frame Acquisition/Maintenance Algorithm per Figure 182.
• FA1, FA2 Octet Search State
• FA1, FA2 Octet Verification State
• OOF Condition State
• LOF Condition State
Each of these Framing Acquisition states, within the Receive E3 Framer Framing Acquisition/Maintenance
State Machine are discussed below.
The FA1, FA2 Octet Search State
When the Receive E3 Framer block is first powered up, it will be operating in the FA1, FA2 Octet Search state.
While the Receive E3 Framer is operating in this state, it will be performing a bit-by-bit search for the FA1 and
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