XRT74L73 Datasheet, PDF (268/488 Pages) Exar Corporation – 3 CHANNEL, ATM UNI/PPP DS3/E3 FRAMING CONTROLLER

XRT74L73
3 CHANNEL, ATM UNI/PPP DS3/E3 FRAMING CONTROLLER
REV. P1.0.1
PRELIMINARY
TABLE 61: 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 XRT74L73 is operated in the serial mode, then the chip will output the payload data, of the
incoming DS3 frames, via this pin. The XRT74L73 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[2:0]
Output Receive Nibble-Parallel Payload Data Output pins:
If the XRT74L73 is operated in the nibble-parallel mode, then the chip will output the payload
data, of the incoming DS3 frames, via these pins. The XRT74L73 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 XRT74L73 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 XRT74L73 will derive this clock signal, from the RxLineClk sig-
nal. The XRT74L73 will pulse this clock 1176 times for each inbound DS3 frame. The Receive
Payload Data Output Interface will update the data, on the RxNib[2:0] output pins upon the fall-
ing edge of this clock signal.
The user is advised to design (or configure) the Terminal Equipment to sample the data on the
RxNib[2:0] 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 XRT74L73 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 XRT74L73 is operating in the Serial
Mode. This output pin will be "Low" if the device is operating in the Nibble-Parallel Mode.
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