XRT74L73 Datasheet, PDF (368/488 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
FIGURE 158. AN ILLUSTRATION OF THE BEHAVIOR OF THE SIGNALS BETWEEN THE RECEIVE PAYLOAD DATA OUT-
PUT INTERFACE BLOCK OF THE XRT74L73 AND THE TERMINAL EQUIPMENT
Terminal Equipment Signals
E3_Clock_In
E3_Data_Out
Rx_Start_of_Frame
E3_Overhead_Ind
Payload[1522] Payload[1523]
FAS , Bit 9
FAS, Bit 8
XRT74L73 Receive Payload Data I/F Signals
RxClk
RxSer
Payload[1522] Payload[1523]
RxFrame
RxOH_Ind
FAS, Bit 9
FAS, Bit 8
E3 Frame Number N
E3 Frame Number N + 1
Note: RxFrame pulses high to denote
E3 Frame Boundary.
Note: RxOH_ Ind pulses high for 12
bit-periods in order to denote
Overhead Data (e.g., the FAS pattern,
the A and N bits).
Note:
FAS pattern will not be processed by
Transmit Paytlohaed Data Input
Interface.
5.3.5.2 Nibble-Parallel Mode Operation Behav-
ior 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 E3 frames, via the RxNib[2:0] output pins, up-
on the rising 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" 1060 times, for each inbound E3
frame.
2. Unlike Serial Mode operation, the duty cycle of
RxClk, in Nibble-Parallel Mode operation is approx-
imately 25%.
Delineation of Inbound E3 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 E3 frame,
via the RxNib[2:0] output pins.
Interfacing the XRT74L73 the Terminal Equip-
ment.
Figure 159 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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