XRT7250 datasheet(236/463 Pages) EXAR

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DS3/E3 FRAMER IC

XRT7250

REV. 1.1.1

217

TABLE 45: LISTING AND DESCRIPTION OF THE PIN ASSOCIATED WITH THE RECEIVE PAYLOAD DATA OUTPUT

INTERFACE BLOCK

SIGNAL NAME

TYPE

DESCRIPTION

RxSer

Output Receive Serial Payload Data Output pin:

If the user opts to operate the XRT7250 in the serial mode, then the chip will output the payload

data, of the incoming DS3 frames, via this pin. The XRT7250 will output this data upon the rising

edge of RxClk.

The user is advised to design the Terminal Equipment such that it will sample this data on the

falling edge of RxClk.

This signal is only active if the NibInt input pin is pulled "Low".

RxNib[3:0]

Output Receive Nibble-Parallel Payload Data Output pins:

If the user opts to operate the XRT7250 in the nibble-parallel mode, then the chip will output the

payload data, of the incoming DS3 frames, via these pins. The XRT7250 will output data via

these pins, upon the falling edge of the RxClk output pin.

The user is advised to design the Terminal Equipment such that it will sample this data upon the

rising edge of RxClk.

These pins are only active if the NibInt input pin is pulled "High".

RxClk

Output Receive Payload Data Output Clock pin:

The exact behavior of this signal depends upon whether the XRT7250 is operating in the Serial

or in the Nibble-Parallel-Mode.

Serial Mode Operation

In the serial mode, this signal is a 44.736MHz clock output signal. The Receive Payload Data

Output Interface will update the data via the RxSer output pin, upon the rising edge of this clock

signal.

The user is advised to design (or configure) the Terminal Equipment to sample the data on the

RxSer pin, upon the falling edge of this clock signal.

Nibble-Parallel Mode Operation

In this Nibble-Parallel Mode, the XRT7250 will derive this clock signal, from the RxLineClk signal.

The XRT7250 will pulse this clock 1176 times for each inbound DS3 frame. The Receive Pay-

load Data Output Interface will update the data, on the RxNib[3:0] output pins upon the falling

edge of this clock signal.

The user is advised to design (or configure) the Terminal Equipment to sample the data on the

RxNib[3:0] output pins, upon the rising edge of this clock signal

RxOHInd

Output Receive Overhead Bit Indicator Output:

This output pin will pulse "High" whenever the Receive Payload Data Output Interface outputs an

overhead bit via the RxSer output pin. The purpose of this output pin is to alert the Terminal

Equipment that the current bit, (which is now residing on the RxSer output pin), is an overhead

bit and should not be processed by the Terminal Equipment.

The XRT7250 will update this signal, upon the rising edge of the RxClk signal.

The user is advised to design (or configure) the Terminal Equipment to sample this signal (along

with the data on the RxSer output pin) on the falling edge of the RxClk signal.

For DS3 applications, this output pin is only active if the XRT7250 is operating in the Serial

Mode. This output pin will be "Low" if the device is operating in the Nibble-Parallel Mode.

RxFrame

Output Receive Start of Frame Output Indicator:

The exact behavior of this pin, depends upon whether the XRT7250 has been configured to

operate in the Serial Mode or the Nibble-Parallel Mode.

Serial Mode Operation:

The Receive Section of the XRT7250 will pulse this output pin "High" (for one bit period) when

the Receive Payload Data Output Interface block is driving the very first bit of a given DS3 frame,

onto the RxSer output pin.

Nibble-Parallel Mode Operation:

The Receive Section of the XRT7250 will pulse this output pin "High" (for one nibble period),

when the Receive Payload Data Output Interface is driving the very first nibble of a given DS3

frame, onto the RxNib[3:0] output pins.

XRT7250 Datasheet(PDF) 236 Page - Exar Corporation

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