XRT7250 Datasheet, PDF (34/463 Pages) Exar Corporation – DS3/E3 FRAMER IC

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PIN DESCRIPTION
PIN #
85
NAME
RxNib0
86
RxSer
87
RxAIS
88
RxClk
89
GND
DS3/E3 FRAMER IC
XRT7250
REV. 1.1.1
TYPE
DESCRIPTION
O 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.
O 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".
0 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".
O 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
**** Ground Pin
15