XRT7250 datasheet(333/463 Pages) EXAR

333 / 463 page

XRT7250

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DS3/E3 FRAMER IC

REV. 1.1.1

314

Method 2 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), then it

is expected to do the following.

1. Sample the state of the RxOHFrame signal (e.g.,

the Rx_Start_of_Frame input) on the falling edge

of the RxOutClk clock signal, whenever the RxO-

HEnable output signal is also sampled "High”.

2. Keep track of the number of times that the RxO-

HEnable signal has been sampled "High” since

the last time the RxOHFrame was also sampled

"High”. By doing this, the Terminal Equipment will

be able to keep track of which overhead bit is

being output via the RxOH output pin. Based

upon this information, the Terminal Equipment

will be able to derive some meaning from these

overhead bits.

3. Table 66 relates the number of RxOHEnable out-

put pulses (that have occurred since both the

RxOHFrame and the RxOHEnable pins were

both sampled "High”) to the E3 overhead bit that

is being output via the RxOH output pin.

FIGURE 147. ILLUSTRATION OF HOW TO INTERFACE THE TERMINAL EQUIPMENT TO THE RECEIVE OVERHEAD DATA

OUTPUT INTERFACE BLOCK (FOR METHOD 2).

RxOH

RxOHEnable

RxOutClk

RxOHFrame

E3_OH_In

E3_OH_Enable_In

E3_Clk_In

Rx_Start_of_Frame

Terminal Equipment

XRT7250 E3 Framer IC

XRT7250 Datasheet(PDF) 333 Page - Exar Corporation