XRT7250 datasheet(276/463 Pages) EXAR

276 / 463 page

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XRT7250

DS3/E3 FRAMER IC

REV. 1.1.1

257

3. After the Terminal Equipment has waited the

appropriate number of clock edges (from the

TxOHFrame signal being sampled "High"), it

should assert the TxOHIns input signal. Concur-

rently, the Terminal Equipment should also place

the appropriate value (of the inserted overhead

bit) onto the TxOH signal.

4. The Terminal Equipment should hold both the

TxOHIns input pin "High" and the value of the

TxOH signal, stable until the next rising edge of

TxOHClk is detected.

Case Study: The Terminal Equipment intends to

insert the appropriate overhead bits into the

Transmit Overhead Data Input Interface (using

Method 1) in order to transmit a Yellow Alarm to

the remote terminal equipment.

In this example, the Terminal Equipment intends to in-

sert the appropriate overhead bits, into the Transmit

Overhead Data Input Interface, such that the

XRT7250 will transmit a Yellow Alarm to the remote

terminal equipment. Recall that, for E3, ITU-T G.751

Applications, a Yellow Alarm is transmitted by setting

the "A" bit to "1".

If one assumes that the connection between the Ter-

minal Equipment and the XRT7250 are as illustrated

in Figure 113 then Figure 114 presents an illustration

of the signaling that must go on between the Terminal

Equipment and the XRT7250.

TABLE 49: THE RELATIONSHIP BETWEEN THE NUMBER OF RISING CLOCK EDGES IN TXOHCLK, (SINCE TXOHFRAME

WAS LAST SAMPLED

"HIGH") TO THE E3 OVERHEAD BIT, THAT IS BEING PROCESSED

NUMBER OF RISING CLOCK EDGES IN

TXOHCLK

THE OVERHEAD BIT EXPECTED BY THE

XRT7250

CAN THIS OVERHEAD BIT BE ACCEPTED BY

THE

XRT7250?

0 (Clock edge is coincident with TxO-

HFrame being detected "High”)

FAS Signal - Bit 9

Yes

FAS Signal - Bit 8

Yes

FAS Signal - Bit 7

Yes

FAS Signal - Bit 6

Yes

FAS Signal - Bit 5

Yes

FAS Signal - Bit 4

Yes

FAS Signal - Bit 3

Yes

FAS Signal - Bit 2

Yes

FAS Signal - Bit 1

Yes

FAS Signal - Bit 0

Yes

A Bit

Yes

N Bit

Yes

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