XRT74L74 Datasheet, PDF (482/498 Pages) Exar Corporation – 4 CHANNEL, ATM UNI/PPP DS3/E3 FRAMING CONTROLLER

XRT74L74
4 CHANNEL, ATM UNI/PPP DS3/E3 FRAMING CONTROLLER
REV. P1.1.1
PRELIMINARY
FIGURE 217. THE BEHAVIOR OF THE SIGNALS BETWEEN THE RECEIVE PAYLOAD DATA OUTPUT INTERFACE BLOCK
OF THE XRT74L74 AND THE TERMINAL EQUIPMENT
Terminal Equipment Signals
E3_Clock_In
E3_Data_In
Rx_Start_of_Frame
E3_Overhead_Ind
Payload[1522] Payload[1523]
FAS, Bit 9
FAS, Bit 8
XRT74L74 Receive Payload Data I/F Signals
RxClk
RxSer
Payload[1532] Payload[1533]
RxFrame
RxOH_Ind
FAS, Bit 9
FAS, Bit 8
E3 Frame Number N
Note: RxFrame pulses high to denote
E3 Frame Boundary.
Note: RxOH_Ind pulses high to
denote Overhead Data
(e.g., the FAS, A and N bits).
E3 Frame Number N + 1
Note: FAS, A and N-Bits will not be processed by the
Transmit Payload Data Input Interface.
7.3.5.2 Nibble-Parallel Mode OperationBehav-
ior of the XRT74L74
If the XRT74L74 has been configured to operate in
the Nibble-Parallel Mode, then the XRT74L74 will be-
have as follows.
Payload Data Output
The XRT74L74 will output the payload data of the in-
coming E3 frames, via the RxNib[3:0] output pins, up-
on the rising edge of RxClk.
NOTES:
1. In this case, RxClk will function as the Nibble Clock
signal between the XRT74L74 the Terminal Equip-
ment. The XRT74L74 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 DS3 Frames
The XRT74L74 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[3:0] output pins.
Interfacing the XRT74L74 the Terminal Equip-
ment.
Figure 218 presents a simple illustration as how the
user should interface the XRT74L74 to that terminal
equipment which processes Receive Direction pay-
load data.
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