XRT74L73 Datasheet, PDF (272/488 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 102. ILLUSTRATION OF THE XRT74L73 DS3/E3 FRAMER IC BEING INTERFACED TO THE RECEIVE SECTION
OF THE TERMINAL EQUIPMENT (NIBBLE-MODE OPERATION)
Rx_DS3_Clock_In
DS3_Data_In[2:0]
Rx_Start_of_Frame
11.184 MHz Clock Signal
RxClk
RxNib[2:0]
RxFrame
44.736 MHz
Clock Source
RxLineClk
Terminal Equipment
(Receive Payload Section)
XRT72L5x DS3 Framer
Required Operation of the Terminal Equipment
The XRT74L73 will update the data on the RxNib[2:0]
line, upon the falling edge of RxClk. Hence, the Ter-
minal Equipment should sample the data on the Rx-
Nib[2:0] output pins (or the DS3_Data_In[2:0] input
pins at the Terminal Equipment) upon the rising edge
of RxClk. As the Terminal Equipment samples RxSer
with each rising edge of RxClk it should also be sam-
pling the RxFrame signal.
The Need for Sampling RxFrame
The XRT74L73 will pulse the RxFrame output pin
"High" coincident with it driving the very first nibble of
a given DS3 frame, onto the RxNib[2:0] output pins.
If knowledge of the DS3 Frame Boundaries is impor-
tant for the operation of the Terminal Equipment, then
this is a very important signal for it to sample.
NOTE: For DS3/Nibble-Parallel Mode Operation, none of
the Overhead bits will be output via the RxNib[2:0] output
pins. Hence, the RxOH_Ind output pin will be in-active in
this mode.
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 XRT74L73
and the Terminal Equipment for DS3 Nibble-Mode op-
eration is illustrated in Figure 103 .
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