XRT72L50 Datasheet, PDF (309/471 Pages) Exar Corporation – SINGLE CHANNEL DS3/E3 FRAMER IC WITH HDLC CONTROLLER

áç
XRT72L50
SINGLE CHANNEL DS3/E3 FRAMER WITH HDLC CONTROLLER
REV. 1.2.1
• The Frame Maintenance Mode: In this mode, the Receive E3 Framer block is trying to maintain frame
synchronization with the incoming E3 Frames.
Figure 124 presents a State Machine diagram that depicts the Receive E3 Framer block's E3/ITU-T G.751
Frame Acquisition/Maintenance Algorithm.
5.3.2.1 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 124.
• FAS Pattern Search State
• FAS Pattern 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 FAS Pattern Search State
When the Receive E3 Framer block is first powered up, it will be operating in the FAS Pattern Search state.
While the Receive E3 Framer is operating in this state, it will be performing a bit-by-bit search for the FAS
(Framing Alignment Signal) pattern of, 1111010000. Figure 125, which presents an illustration of the E3, ITU-
T G.751 Framing Format, indicates that this framing alignment signal will occur at the beginning of each E3
frame.
296