XRT7250 datasheet(34/463 Pages) EXAR

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DS3/E3 FRAMER IC

XRT7250

REV. 1.1.1

RxNib0

Receive Nibble Output - 0

The Framer IC will output "Received data (from the Remote Terminal) to the

local Terminal Equipment via this pin along with RxNib1, RxNib2 and RxNib3.

The data at this pin is updated on the rising edge of the RxClk output signal.

NOTE: This output pin is active only if the Nibble-Parallel Mode has been

selected.

RxSer

Receive Serial Output;

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

output the payload data, of the incoming DS3 or E3 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.

NOTE: This signal is only active if the "NibInt" input pin is pulled "low".

RxAIS

Receive "Alarm Indication Signal" Output pin:

The Framer will assert this pin to indicate that the Alarm Indication Signal (AIS)

has been identified in the Receive DS3 or E3 data stream.

For DS3 Applications

The Framer will assert this pin to indicate that the Alarm Indication Signal (AIS)

has been identified in the Receive DS3 data stream. An "AIS" is detected if the

payload consists of the recurring pattern of 1010... and this pattern persists for

63 M-frames. An additional requirement for AIS indication is that the C-bits are

set to 0, and the X-bits are set to 1. This pin will be negated when a sufficient

number of frames, not exhibiting the "1010..." pattern in the payload has been

detected.

For E3 Applications

The Receive Section will declare an AIS condition, if it detects two consecutive

E3 frames, each containing 7 or less "0s".

RxClk

Receive Clock Output Signal for Serial and Nibble/Parallel Data

Interface

The exact behavior of this signal depends upon whether the XRT7250 is oper-

ating 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 (for DS3

applications) or 34.368MHz clock output signal (for E3 applications). The

Receive Payload Data Output Interface will update the data via the RxSer out-

put 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 signal 1176 times for each

"inbound" DS3 frame (or 1074 times for each inbound “E3/ITU-T G.832” frame,

or 384 times for each inbound “E3/ITU-T G.751 frame). The Receive Payload

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 sig-

nal

GND

****

Ground Pin

PIN DESCRIPTION

PIN #NAME

TYPE

DESCRIPTION

XRT7250 датащи(PDF) 34 Page - Exar Corporation

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