XRT7250 datasheet(175/463 Pages) EXAR

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XRT7250

DS3/E3 FRAMER IC

áç

REV. 1.1.1

156

b. Set the TxOH input to 0.

Once again, after the Terminal Equipment has ap-

plied these signals, the XRT7250 will sample the data

on both the TxOHIns and TxOH signal upon the very

next falling edge of TxOHClk (designated as 8- in

Figure 58). Once the XRT7250 has sampled this da-

ta, it will then insert a "0" into the second X bit posi-

tion, in the outbound DS3 frame.

4.2.2.2

Method 2 - Using the TxInClk and TxO-

HEnable 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 accommodate and

process 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 sam-

ple the overhead bits and signals which are input to

the Transmit Overhead Data Input Interface. Method

2 involves the use of the following signals:

• TxOH

• TxInClk

• TxOHFrame

• TxOHEnable

Each of these signals are listed and described in

Table 22.

Interfacing the Transmit Overhead Data Input Interface

to the Terminal Equipment

Figure 59 illustrates how one should interface the

Transmit Overhead Data Input Interface to the Termi-

nal Equipment when using Method 2.

TABLE 22: DESCRIPTION OF METHOD 2 TRANSMIT OVERHEAD INPUT INTERFACE SIGNALS

NAME

TYPE

DESCRIPTION

TxOHEnable

Output

Transmit Overhead Data Enable Output pin

The XRT7250 will assert this signal, for one TxInClk period, just prior to the instant that

the Transmit Overhead Data Input Interface is processing an overhead bit.

TxOHFrame

Output

Transmit Overhead Input Interface Frame Boundary Indicator Output:

This output signal pulses "High" when the XRT7250 is processing the last bit within a

given DS3 frame.

TxOHIns

Input

Transmit Overhead Data Insert Enable input pin.

Asserting this input signal (e.g., setting it "High") enables the Transmit Overhead Data Input Inter-

face to accept overhead data from the Terminal Equipment. In other words, while this input pin is

"High", the Transmit Overhead Data Input Interface will sample the data at the TxOH input pin, on

the falling edge of the TxInClk output signal.

Conversely, setting this pin "Low" configures the Transmit Overhead Data Input Interface to NOT

sample (e.g., ignore) the data at the TxOH input pin, on the falling edge of the TxOHClk output

signal.

NOTE: If the Terminal Equipment attempts to insert an overhead bit that cannot be accepted by

the Transmit Overhead Data Input Interface (e.g., if the Terminal Equipment asserts the TxOHIns

signal, at a time when one of these non-insertable overhead bits are being processed), that par-

ticular insertion effort will be ignored.

TxOH

Input

Transmit Overhead Data Input pin:

The Transmit Overhead Data Input Interface accepts the overhead data via this input

pin, and inserts into the overhead bit position within the very next outbound DS3 frame.

If the TxOHIns pin is pulled "High", the Transmit Overhead Data Input Interface will sam-

ple the data at this input pin (TxOH), on the falling edge of the TxOHClk output pin.

Conversely, if the TxOHIns pin is pulled "Low", then the Transmit Overhead Data Input

Interface will NOT sample the data at this input pin (TxOH). Consequently, this data will

be ignored.

XRT7250 Datasheet(PDF) 175 Page - Exar Corporation

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