XRT7250 datasheet(239/463 Pages) EXAR

239 / 463 page

XRT7250

DS3/E3 FRAMER IC

áç

REV. 1.1.1

220

the very first nibble, within a given inbound DS3

frame, via the RxNib[3:0] output pins.

Interfacing the XRT7250 the Terminal Equipment.

Figure 95 presents a simple illustration as how the

user should interface the XRT7250 to that terminal

equipment which processes Receive Direction pay-

load data.

Required Operation of the Terminal Equipment

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

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

minal Equipment should sample the data on the Rx-

Nib[3:0] output pins (or the DS3_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 DS3 frame, onto the RxNib[3:0] output pins.

If knowledge of the DS3 Frame Boundaries is impor-

tant for the operation of the Terminal Equipment, then

this is a very important signal for it to sample.

NOTE: For DS3/Nibble-Parallel Mode Operation, none of

the Overhead bits will be output via the RxNib[3:0] output

pins. Hence, the RxOH_Ind output pin will be in-active in

this mode.

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 DS3 Nibble-Mode op-

eration is illustrated in Figure 96.

FIGURE 95. ILLUSTRATION OF THE XRT7250 DS3/E3 FRAMER IC BEING INTERFACED TO THE RECEIVE SECTION OF

THE

TERMINAL EQUIPMENT (NIBBLE-MODE OPERATION)

Terminal Equipment

(Receive Payload Section)

XRT7250 DS3 Framer

DS3_Data_In[3:0]

Rx_DS3_Clock_In

Rx_Start_of_Frame

RxClk

RxFrame

11.184 MHz Clock Signal

RxNib[3:0]

RxLineClk

44.736 MHz

Clock Source

XRT7250 Datasheet(PDF) 239 Page - Exar Corporation

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