XRT7250 datasheet(278/463 Pages) EXAR

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XRT7250

DS3/E3 FRAMER IC

REV. 1.1.1

259

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-

head 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 50.

Interfacing the Transmit Overhead Data Input Interface

to the Terminal Equipment

Figure 115 illustrates how one should interface the

Transmit Overhead Data Input Interface to the Termi-

nal Equipment when using Method 2.

TABLE 50: DESCRIPTION OF METHOD 2 TRANSMIT OVERHEAD INPUT INTERFACE SIGNALS

NAME

TYPE

DESCRIPTION

TxOHEn-

able

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.

TxO-

HFrame

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

Interface 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 sample 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) 278 Page - Exar Corporation

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