XRT7250 datasheet(27/463 Pages) EXAR

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XRT7250

DS3/E3 FRAMER IC

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REV. 1.1.1

TxOHClk

Transmit Overhead Clock

This output signal serves two purposes:

1. The Transmit Overhead Data Input Interface block will provide a rising clock

edge on this signal, one bit-period prior to the start to the instant that the

“Transmit Overhead Data Input Interface” block is processing an overhead bit.

2. The Transmit Overhead Data Input Interface will sample the data at the

“TxOH” input pin, on the falling edge of this clock signal (provided that the

“TxOHIns” input pin is “HIGH”).

NOTE: The Transmit Overhead Data Input Interface block will supply a clock

edge for all overhead bits within the DS3 or E3 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.

TxOHIns

Transmit Overhead Data Insert Input.

Asserting this input signal (e.g., setting it "high") enables the Transmit Over-

head Data Input Interface to accept "overhead" data from the Terminal Equip-

ment. 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 Termi-

nal Equipment asserts the "TxOHIns" signal, at a time when one of these "non-

insertable" overhead bits are being processed); that particular insertion effort

will be ignored.

TxOH

Transmit Overhead 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 "out-

bound" DS3 or E3 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

TxOHInd

Transmit Overhead Data Indicator.

This output pin will pulse "high" one-bit period prior to the time that the Transmit

Section of the XRT7250 will be processing an Overhead bit. The purpose of

this output pin is to warn the Terminal Equipment that, during the very next bit-

period, the XRT7250 is going to be processing an "Overhead" bit and will be

ignoring any data that is applied to the "TxSer" input pin.

NOTE: For DS3 applications, this output pin is only active if the XRT7250 is

operating in the "Serial" Mode. This output pin will be pulled "low" if the device

is operating in the "Nibble-Parallel" Mode.

PIN DESCRIPTION

PIN #NAME

TYPE

DESCRIPTION

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