XRT7250 datasheet(309/463 Pages) EXAR

309 / 463 page

XRT7250

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DS3/E3 FRAMER IC

REV. 1.1.1

290

• The Frame Acquisition Mode: In this mode, the

Receive E3 Framer block is trying to acquire syn-

chronization 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 136 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 op-

erating in the Frame Acquisition Mode, if it is operat-

ing in any one of the following states within the E3

Frame Acquisition/Maintenance Algorithm per

Figure 136.

• 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 137, which presents an illus-

tration of the E3, ITU-T G.751 Framing Format, indi-

cates that this framing alignment signal will occur at

the beginning of each E3 frame.

XRT7250 Datasheet(PDF) 309 Page - Exar Corporation