XRT72L13 Datasheet, PDF (337/370 Pages) Exar Corporation – M13 MULTIPLEXER/CLEAR CHANNEL DS3 FRAMER IC

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PRELIMINARY
XRT72L13
M13 MULTIPLEXER/CLEAR CHANNEL DS3 FRAMER IC
REV. P1.0.6
The XRT72L13 will pulse the "RxFrame" output pin
"high" coincident with it driving the very first bit of a
given DS3 frame onto the "RxSer" output pin. 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.
The Need for sampling "RxOHInd"
The XRT72L13 will indicate that it is currently driving
an "overhead" bit onto the "RxSer" output pin, by
pulsing the "RxOHInd" output pin "high". If the Termi-
nal Equipment samples this signal "high", then it
should know 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 XRT72L13
and the Terminal Equipment for DS3 Serial Mode Op-
eration is illustrated in Figure 113 .
FIGURE 113. AN ILLUSTRATION OF THE BEHAVIOR OF THE SIGNALS BETWEEN THE "RECEIVE PAYLOAD DATA OUT-
PUT INTERFACE" BLOCK (OF THE XRT72L13) 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]
XRT72L13 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.
4.3.5.2 Nibble-Parallel Mode Operation
Behavior of the XRT72L13
If the XRT72L13 has been configured to operate in
the "Nibble-Parallel" Mode, then the XRT72L13 will
behave as follows.
Payload Data Output
The XRT72L13 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 XRT72L13 the Terminal
Equipment. The XRT72L13 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
approximately 25%.
Delineation of "Inbound" DS3 Frames
325