XRT7250 datasheet(432/463 Pages) EXAR

432 / 463 page

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XRT7250

DS3/E3 FRAMER IC

REV. 1.1.1

413

Within the Receive Section of the XRT7250, the Re-

ceive Payload Data Output Interface block has been

designed to handle the payload bits. Likewise, the

Receive Overhead Data Output Interface block has

been designed to handle and process the overhead

bits.

The Receive Overhead Data Output Interface block

unconditionally outputs the contents of all overhead

bits. The XRT7250 does not offer the user a means

to shut off this transmission of data. However, the

Receive Overhead Output Interface block does pro-

vide the user with the appropriate output signals for

external Data Link Layer equipment to sample and

process these overhead bits, via the following two

methods.

• Method 1- Using the RxOHClk clock signal.

• Method 2 - Using the RxClk and RxOHEnable out-

put signals.

Each of these methods are described below.

6.3.4.1

Method 1 - Using the RxOHClk Clock

signal

The Receive Overhead Data Output Interface block

consists of four (4) signals. Of these four signals, the

following three signals are to be used when sampling

the E3 overhead bits via Method 1.

• RxOH

• RxOHClk

• RxOHFrame

Each of these signals are listed and described below

in Table 87.

Interfacing the Receive Overhead Data Output In-

terface block to the Terminal Equipment (Method

Figure 204 illustrates how one should interface the

Receive Overhead Data Output Interface block to the

Terminal Equipment when using Method 1, to sample

and process the overhead bits from the Inbound E3

data stream.

Method 1 Operation of the Terminal Equipment

If the Terminal Equipment intends to sample any

overhead data from the Inbound E3 data stream (via

the Receive Overhead Data Output Interface block)

then it is expected to do the following:

FIGURE 204. ILLUSTRATION OF HOW TO INTERFACE THE TERMINAL EQUIPMENT TO THE RECEIVE OVERHEAD DATA

OUTPUT INTERFACE BLOCK (FOR METHOD 1).

Terminal Equipment

XRT7250 E3 Framer IC

RxOHClk

E3_OH_Clock_In

RxOH

RxOHFrame

E3_OH_In

Rx_Start_of_Frame

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