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PRELIMINARY
XRT79L71
254
REV. P2.0.0
1-CHANNEL DS3/E3 CLEAR-CHANNEL FRAMERLIU COMBO - CC/HDLC ARCHITECTURE
will output this data upon the rising edge of the RxCLK signal. As a consequence, the user is advised to
design or configure the System-Side Terminal Equipment circuitry to sample and latch this data via the
DS3_Data_In input pin upon the falling edge of RxCLK (Rx_DS3_Clock_In), as depicted below in Figure 107.
The Receive Payload Data Output Interface block within the XRT79L71 will indicate that it is processing the
very first bit of a given DS3 frame by pulsing the RxFrame output pin "High" for one bit-period. The RxFrame
output pin will be held "Low" at all other times.
Finally, the Receive Payload Data Output Interface block within the XRT79L71 permits the System-Side
Terminal Equipment to identify a given bit that is being output via the RxSer output pin as either an overhead or
a payload bit by pulsing the RxOH_Ind output pin "High" for one bit-period coincident to whenever the Receive
Payload Data Output Interface block outputs an overhead bit via the RxSer output pin.
Conversely, the
Receive Payload Data Output Interface block will hold the RxOH_Ind output pin "Low" coincident to whenever
the Receive Payload Data Output Interface block outputs a payload bit via the RxSer output pin.
Figure 108 presents an illustration of the System-Side Terminal Equipment/Receive Payload Data Output
Interface signal for Serial Mode Operation.
Configuring the XRT79L71 to operate in Serial Mode.
The user can configure the XRT79L71 to operate in the Serial Mode by executing the following steps.
STEP 1 - Design your board such that the System-Side Terminal Equipment circuitry interfaces to the
Receive Payload Data Input Interface in the manner as depicted above in Figure 107. STEP 2 - Configure the XRT79L71 to operate in the Serial Mode
This can be accomplished by setting the NibIntf input pin to a logic "Low".
NOTE: This step also configures the Transmit Payload Data Input Interface block to operate in the Serial Mode.
Operating the Receive Payload Data Output Interface in the Non-Gapped Clock Mode
FIGURE 108. AN ILLUSTRATION OF THE BEHAVIOR OF THE SYSTEM-SIDE TERMINAL EQUIPMENT SIGNALS FOR
SERIAL MODE OPERATION
System-Side Terminal Equipment Signals
DS3_Clock_In
DS3_Data_In
Rx_Start_of_Frame
DS3_Overhead_Ind
XRT79L71 Receive Payload Data Output Interface Signals
RxClk
RxSer
RxFrame
RxOH_Ind
Payload[4702]
Payload[4703]
X-Bit
Payload[0]
Payload[4702]
Payload[4703]
X-Bit
Payload[0]
DS3 Frame Number N
DS3 Frame Number N + 1
Note: RxFrame pulses high to denote
DS3 Frame Boundary.
Note: RxOH_Ind pulses high to
denote Overhead Data
(e.g., the X-bit).