XRT7250 datasheet(170/463 Pages) EXAR

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DS3/E3 FRAMER IC

XRT7250

REV. 1.1.1

151

• TxOHIns

Each of these signals are listed and described below.

Table 20.

Interfacing the Transmit Overhead Data Input In-

terface to the Terminal Equipment.

Figure 57 illustrates how one should interface the

Transmit Overhead Data Input Interface to the Termi-

nal Equipment, when using Method 1.

TABLE 20: DESCRIPTION OF METHOD 1 TRANSMIT OVERHEAD INPUT INTERFACE SIGNALS

NAME

TYPE

DESCRIPTION

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 TxOHClk 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.

TxOHClk

Output

Transmit Overhead Input Interface Clock Output signal:

This output signal serves two purposes:

1. The Transmit Overhead Data Input Interface will provide a rising clock edge on this signal, one

bit-period prior to the instant that the Transmit Overhead Data Input Interface is processing an

overhead bit.

2. The Transmit Overhead Data Input Interface will sample the data at the TxOH input, on the fall-

ing edge of this clock signal (provided that the TxOHIns input pin is "High").

NOTE: The Transmit Overhead Data Input Interface will supply a clock edge for all overhead bits

within the DS3 frame (via the TxOHClk output signal). This includes those overhead bits that the

Transmit Overhead Data Input Interface will not accept from the Terminal Equipment.

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.

The purpose of this output signal is to alert the Terminal Equipment that the Transmit

Overhead Data Input Interface block is about to begin processing the overhead bits for a

new DS3 frame.

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