XR72L52 Datasheet, PDF (421/480 Pages) Exar Corporation – TWO CHANNEL DS3/E3 FRAMER IC WITH HDLC CONTROLLER

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TWO CHANNEL DS3/E3 FRAMER IC WITH HDLC CONTROLLER
XRT72L52
REV. 1.0.1
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 synchroniza-
tion with the incoming E3 frame, or
• The Frame Maintenance Mode: In this mode, the Receive E3 Framer block is trying to maintain frame syn-
chronization 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
FA2 Framing Alignment octets. FA1 is assigned the value 0xF6, and FA2 is assigned the value of 0x28.
Figure 183, which presents an illustration of the E3, ITU-T G.832 Framing Format, indicates that these two oc-
tets will occur at the beginning of each E3 frame, and that the FA2 octet will appear immediately after the FA1
octet.
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