XRT7250 datasheet(339/463 Pages) EXAR

339 / 463 page

XRT7250

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DS3/E3 FRAMER IC

REV. 1.1.1

320

Required Operation of the Terminal Equipment

The XRT7250 will update the data on the RxNib[3:0]

line, upon the rising edge of RxClk. Hence, the Ter-

minal Equipment should sample the data on the Rx-

Nib[3:0] output pins (or the E3_Data_In[3:0] input

pins at the Terminal Equipment) upon the rising edge

of RxClk. As the Terminal Equipment samples RxSer

with each rising edge of RxClk it should also be sam-

pling the RxFrame signal.

The Need for Sampling RxFrame

The XRT7250 will pulse the RxFrame output pin

"High" coincident with it driving the very first nibble of

a given E3 frame, onto the RxNib[3:0] output pins. If

knowledge of the E3 Frame Boundaries is important

for the operation of the Terminal Equipment, then this

is a very important signal for it to sample.

The Behavior of the Signals between the Receive

Payload Data Output Interface block and the Ter-

minal Equipment

The behavior of the signals between the XRT7250

and the Terminal Equipment for E3 Nibble-Mode op-

eration is illustrated in Figure 153.

FIGURE 152. ILLUSTRATION OF THE XRT7250 DS3/E3 FRAMER IC BEING INTERFACED TO THE RECEIVE SECTION

OF THE

TERMINAL EQUIPMENT (NIBBLE-PARALLEL MODE OPERATION)

Terminal Equipment

(Receive Payload Section)

XRT7250 E3 Framer

E3_Data_In[3:0]

Rx_E3_Clock_In

Rx_Start_of_Frame

RxClk

RxFrame

8.592 MHz Clock Signal

RxNib[3:0]

RxLineClk

34.368 MHz

Clock Source

RxOH_Ind

Rx_E3_OH_Ind

XRT7250 Datasheet(PDF) 339 Page - Exar Corporation

XRT7250 Datasheet(HTML) 339 Page - Exar Corporation

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