XRT74L73 Datasheet, PDF (271/488 Pages) Exar Corporation – 3 CHANNEL, ATM UNI/PPP DS3/E3 FRAMING CONTROLLER

PRELIMINARY
XRT74L73
3 CHANNEL, ATM UNI/PPP DS3/E3 FRAMING CONTROLLER
REV. P1.0.1
FIGURE 101. AN ILLUSTRATION OF THE BEHAVIOR OF THE SIGNALS BETWEEN THE RECEIVE PAYLOAD DATA OUT-
PUT INTERFACE BLOCK OF THE XRT74L73 AND THE TERMINAL EQUIPMENT (SERIAL MODE OPERATION)
Terminal Equipment Signals
DS3_Clock_In
DS3_Data_In
Rx_Start_of_Frame
DS3_Overhead_Ind
Payload[4702] Payload[4703]
X-Bit
Payload[0]
XRT72L5x Receive Payload Data I/F Signals
RxClk
RxSer
Payload[4702] Payload[4703]
RxFrame
RxOH_Ind
X-Bit
Payload[0]
DS3 Frame Number N
Note: RxFrame pulses high to denote
DS3 Frame Boundary.
Note: RxOH_Ind pulses high to
denote Overhead Data
(e.g., the X-bit).
DS3 Frame Number N + 1
Note: X-Bit will not be processed by the
Transmit Payload Data Input Interface.
4.3.5.2 Nibble-Parallel Mode Operation
Behavior of the XRT74L73
If the XRT74L73 has been configured to operate in
the Nibble-Parallel Mode, then the XRT74L73 will be-
have as follows.
Payload Data Output
The XRT74L73 will output the payload data of the in-
coming DS3 frames, via the RxNib[2:0] output pins,
upon the falling edge of RxClk.
NOTES:
1. In this case, RxClk will function as the Nibble Clock
signal between the XRT74L73 the Terminal Equip-
ment. The XRT74L73 will pulse the RxClk output
signal "High" 1176 times, for each inbound DS3
frame.
2. Unlike Serial Mode operation, the duty cycle of
RxClk, in Nibble-Parallel Mode operation is approx-
imately 25%.
Delineation of Inbound DS3 Frames
The XRT74L73 will pulse the RxFrame output pin
"High" for one nibble-period coincident with it driving
the very first nibble, within a given inbound DS3
frame, via the RxNib[2:0] output pins.
Interfacing the XRT74L73 the Terminal Equip-
ment.
Figure 102 presents a simple illustration as how the
user should interface the XRT74L73 to that terminal
equipment which processes Receive Direction pay-
load data.
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