XRT7250 datasheet(379/463 Pages) EXAR

379 / 463 page

XRT7250

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DS3/E3 FRAMER IC

REV. 1.1.1

360

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 Applications,

a Yellow Alarm is transmitted by setting the FERF bit

(within the MA Byte) to "0".

If one assumes that the connection between the Ter-

minal Equipment and the XRT7250 are as illustrated

in Figure 170 then Figure 171 presents an illustration

of the signaling that must go on between the Terminal

Equipment and the XRT7250.

In Figure 171 the Terminal Equipment samples the

TxOHFrame signal being "High" at rising clock edge #

“0". From this point, the Terminal Equipment waits

until it has detected 32 rising edges in the TxOHClk

signal. At this point, the Terminal Equipment knows

that the XRT7250 is just about to process the FERF

bit within the MA byte (in a given Outbound E3

frame). Additionally, according to Table 73, the 32nd

overhead bit to be processed is the FERF bit. In or-

der to facilitate the transmission of the Yellow Alarm,

the Terminal Equipment must set this FERF bit to "1".

Hence, the Terminal Equipment starts this process by

implementing the following steps concurrently.

a. Assert the TxOHIns input pin by setting it "High".

b. Set the TxOH input pin to "0".

After the Terminal Equipment has applied these sig-

nals, the XRT7250 will sample the data on both the

TxOHIns and TxOH signals upon the very next falling

edge of TxOHClk (designated at 32- in Figure 171).

Once the XRT7250 has sampled this data, it will then

insert a "1" into the FERF bit position, in the Out-

bound E3 frame.

Upon detection of the very next rising edge of the Tx-

OHClk clock signal (designated as clock edge 1 in

Figure 171), the Terminal Equipment will negate the

TxOHIns signal (e.g., toggles it "Low") and will cease

inserting data into the Transmit Overhead Data Input

Interface.

6.2.2.2

Method 2 - Using the TxInClk and

TxOHEnable Signals

Method 1 requires the use of an additional clock sig-

nal, TxOHClk. However, there may be a situation in

which the user does not wish to add this extra clock

signal to their design, in order to use the Transmit

Overhead Data Input Interface. Hence, Method 2 is

available. When using Method 2, either the TxInClk

or RxOutClk signal is used to sample the overhead

bits and signals which are input to the Transmit Over-

FIGURE 171. ILLUSTRATION OF THE SIGNAL THAT MUST OCCUR BETWEEN THE TERMINAL EQUIPMENT AND THE

XRT7250, IN ORDER TO CONFIGURE THE XRT7250 TO TRANSMIT A YELLOW ALARM TO THE REMOTE TERMINAL

EQUIPMENT

Terminal Equipment/XRT7250 Interface Signals

TxOHClk

TxOHIns

TxOHFrame

TxOH

Remaining Overhead Bits with E3 Frame

MA, Bit 7

TxOHFrame is sample “high”

Terminal Equipment asserts TxOHIns and

Data on TxOH line.

XRT7250 Framer device samples TxOHIns and

TxOHIns signal

XRT7250 Datasheet(PDF) 379 Page - Exar Corporation

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