XRT74L74 Datasheet, PDF (282/498 Pages) Exar Corporation – 4 CHANNEL, ATM UNI/PPP DS3/E3 FRAMING CONTROLLER

XRT74L74
REV. P1.1.1
4 CHANNEL, ATM UNI/PPP DS3/E3 FRAMING CONTROLLER
ADVANCED CONFIDENTIAL
that the bit, that it is currently sampling via the RxSer
pin is an overhead bit and should not be processed.
The Behavior of the Signals between the Receive
Payload Data Output Interface block and the Ter-
minal Equipment
The behavior of the signals between the XRT74L74
and the Terminal Equipment for DS3 Serial Mode Op-
eration is illustrated in Figure 101.
FIGURE 101. AN ILLUSTRATION OF THE BEHAVIOR OF THE SIGNALS BETWEEN THE RECEIVE PAYLOAD DATA OUT-
PUT INTERFACE BLOCK OF THE XRT74L74 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.
5.3.5.2 Nibble-Parallel Mode Operation
Behavior 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 DS3 frames, via the RxNib[3:0] output pins,
upon the falling 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" 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 XRT74L74 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[3:0] output pins.
Interfacing the XRT74L74 the Terminal Equip-
ment.
Figure 102 presents a simple illustration as how the
user should interface the XRT74L74 to that terminal
equipment which processes Receive Direction pay-
load data.
280