XRT7250 datasheet(359/463 Pages) EXAR

359 / 463 page

XRT7250

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DS3/E3 FRAMER IC

REV. 1.1.1

340

Mode 1 Operation of the Terminal Equipment

When the XRT7250 is operating in this mode it will

function as the source of the 34.368MHz clock signal.

This clock signal will be used as the Terminal Equip-

ment Interface clock by both the XRT7250 IC and the

Terminal Equipment.

The Terminal Equipment will serially output the pay-

load data of the Outbound E3 data stream via its

E3_Data_Out pin. The Terminal Equipment will up-

date the data on the E3_Data_Out pin upon the rising

edge of the 34.368 MHz clock signal, at its

E3_Clock_In input pin (as depicted in Figures 19 and

20).

The XRT7250 will latch the Outbound E3 data stream

(from the Terminal Equipment) on the rising edge of

the RxOutClk signal.

The XRT7250 will indicate that it is processing the

last bit, within a given Outbound E3 frame, by pulsing

its TxFrame output pin “High” for one bit-period.

When the Terminal Equipment detects this pulse at its

Tx_Start_of_Frame input, it is expected to begin

transmission of the very next Outbound E3 frame to

the XRT7250 via the E3_Data_Out (or TxSer pin).

Finally, the XRT7250 will indicate that it is about to

process an overhead bit by pulsing the TxOH_Ind

output pin "High" one bit period prior to its processing

of an OH (Overhead) bit. In Figure 157, the

TxOH_Ind output pin is connected to the

E3_Overhead_Ind input pin, of the Terminal Equip-

ment. Whenever the E3_Overhead_Ind pin is pulsed

"High" the Terminal Equipment is expected to not

transmit a E3 payload bit upon the very next clock

edge. Instead, the Terminal Equipment is expected to

delay its transmission of the very next payload bit, by

one clock cycle.

The behavior of the signals, between the XRT7250

and the Terminal Equipment, for E3 Mode 1 operation

is illustrated in Figure 158.

FIGURE 157. ILLUSTRATION OF THE TERMINAL EQUIPMENT BEING INTERFACED TO THE TRANSMIT PAYLOAD DATA

INPUT INTERFACE BLOCK OF THE XRT7250 FOR MODE 1 (SERIAL/LOOP-TIMED) OPERATION

Terminal Equipment

XRT7250 E3 Framer

E3_Data_Out

E3_Clock_In

Tx_Start_of_Frame

E3_Overhead_Ind

TxSer

RxOutClk

TxFrame

TxOH_Ind

NibInt

34.368 MHz

XRT7250 Datasheet(PDF) 359 Page - Exar Corporation

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