XRT7250 datasheet(28/463 Pages) EXAR

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DS3/E3 FRAMER IC

XRT7250

REV. 1.1.1

TxOHEnable

Transmit Overhead Input Enable.

The XRT7250 will assert this signal, for one “TxInClk” period, just prior to the

instant that the “Transmit Overhead Data Input Interface” will be sampling and

processing an overhead bit.

If the Terminal Equipment intends to insert its own value for an overhead bit,

into the outbound DS3 or E3 frame, it is expected to sample the state of this

signal, upon the falling edge of “TxInClk”. Upon sampling the “TxOHEnable”

high, the Terminal Equipment should (1) place the desired value of the over-

head bit, onto the “TxOH” input pin and (2) assert the “TxOHIns” input pin. The

Transmit Overhead Data Input Interface” block will sample and latch the data

on the “TxOH” signal, upon the rising edge of the very next “TxInClk” input sig-

nal.

TxOHFrame

Transmit Overhead Framing Pulse:

This output pin pulses "high" when the Transmit Overhead Data Input Interface

block is expecting the first Overhead bit, within a DS3 or E3 frame to be applied

to the TxOH input pin.

This pin is "high" for one clock period of TxOHClk.

TxNibFrame

Transmit Frame Boundary Indicator - Nibble/Parallel Interface

This output pin pulses "high" when the last nibble of a given DS3 or E3 frame is

expected at the TxNib[3:0] input pins.

The purpose of this output pin is to alert the Terminal Equipment that it needs

to begin transmission of a new DS3 or E3 frame to the XRT7250.

TxNibClk

Transmit Nibble Clock Signal

If the user opts to operate the XRT7250 in the “Nibble-Parallel” mode,

then the XRT7250 will derive this clock signal from either the “TxInClk”

or the “RxLineClk” signal (depending upon which signal is selected as

the timing reference).

The user is advised to configure the Terminal Equipment to output the

“outbound” payload data (to the XRT7250 Framer IC) onto the “Tx-

Nib[3:0]” input pins, upon the rising edge of this clock signal.

NOTES:

1. For DS3 applications, the XRT7250 Framer IC will output 1176 clock

edges (to the Terminal Equipment) for each “outbound” DS3 frame.

2. For E3, ITU-T G.832 applications, the XRT7250 Framer IC will output

1074 clock edges (to the Terminal Equipment) for each “outbound” E3

frame.

3. For E3, ITU-T G.751 applications, the XRT7250 Framer IC will output

384 clock edges (fo the Terminal Equipment) for each “outbound” E3

frame.

GND

****

Ground Pin

TxFrame

Transmit End of DS3 or E3 Frame Indicator:

The Transmit Section of the XRT7250 will pulse this output pin "high" (for one

bit-period), when the Transmit Payload Data Input Interface is processing the

last bit of a given DS3 or E3 frame.

The purpose of this output pin is to alert the Terminal Equipment that it needs

to begin transmission of a new DS3 or E3 frame to the XRT7250 (e.g., to per-

mit the XRT7250 to maintain Transmit DS3/E3 framing alignment control over

the Terminal Equipment).

VDD

****

Power Supply pin

PIN DESCRIPTION

PIN #NAME

TYPE

DESCRIPTION

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