XRT74L73 Datasheet, PDF (369/488 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 159. THE XRT74L73 DS3/E3 FRAMER IC BEING INTERFACED TO THE RECEIVE SECTION OF THE TERMINAL
EQUIPMENT (NIBBLE-PARALLEL MODE OPERATION)
Rx_E3_Clock_In
E3_Data_In[2:0]
Rx_Start_of_Frame
Rx_E3_OH_Ind
8.592MHz
Clock Signal
RxClk
RxNib[2:0]
RxLineClk
RxFrame
RxOH_Ind
34.368MHz
Clock Source
Terminal Equipment
Receive Payload Section
XRT74L73 E3 Framer
Required Operation of the Terminal Equipment
The XRT74L73 will update the data on the RxNib[2:0]
line, upon the rising edge of RxClk. Hence, the Ter-
minal Equipment should sample the data on the Rx-
Nib[2:0] output pins (or the E3_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 E3 frame, onto the RxNib[2:0] output pins. If
knowledge of the E3 Frame Boundaries is important
for the operation of the Terminal Equipment, then this
is a very important signal for it to sample.
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 E3 Nibble-Mode op-
eration is illustrated in Figure 160 .
370