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PRELIMINARY
XRT79L71
448
REV. P2.0.0
1-CHANNEL DS3/E3 CLEAR-CHANNEL FRAMERLIU COMBO - CC/HDLC ARCHITECTURE
The XRT79L71 will be configured to operate in the Local-Timing Mode. In other words, the Transmit Section
of the XRT79L71 will use the "TxInClk" input signal has its timing source.
In this mode, the XRT79L71 will use the TxInClk signal to derive the "TxNibClk" signal.
For E3 Applications, the "TxNibClk" frequency is exactly one-fourth of the "TxInClk" clock input signal (or
8.592MHz).
Since the XRT79L71 is configured to operate in the "Nibble-Parallel" Mode, it will sample and latch the data,
being applied to the "TxNib[3:0]" input pins upon the third rising edge of the "TxInClk" input clock signal,
following a given rising edge of the "TxNibClk" output clock signal.
The Transmit Section of the XRT79L71 will initiate the generate and transmission of a new E3 frame anytime
it detects a rising edge in the "TxFrameRef" input pin.
The XRT79L71 will pulse the "TxNibFrame" output pin "high" for one nibble-period coincident to whenever
the Transmit Payload Data Input Interface is processing the very last nibble within a given E3 frame.
Mode 5 Operation of the Transmit Payload Data Input Interface Block
Whenever the XRT79L71 has been configured to operate in this mode, it will function as the source of a Nibble
Clock signal (via the "TxNibClk" output signal).
NOTE: For "Mode 5" Operation, the "TxNibClk" output signal is ultimately derived from the "TxInClk" input signal.
The "System-Side Terminal Equipment" should output the payload data (that is to be transported via the
"outbound" E3 data-stream) in a "Nibble-Parallel" manner via its "E3_Data_Out[3:0]" output pins. The user is
advised to design (or configure) the System-Side Terminal Equipment circuitry such that it will update the data
(via the "E3_Data_Out[3:0]" output pins) upon the rising edge of the "TxNibClk" clock signal (at its
"E3_Nib_Clock_In" input pin) as depicted below in Figure 215.
The XRT79L71 will latch the contents of the "TxNib[3:0]" input pins, upon the third rising edge of the "TxInClk"
signal following a given rising edge in the "TxNibClk" signal. In this particular mode, the System-Side Terminal
Equipment also has the responsibility of providing a "Framing Reference" signal to the XRT79L71 by pulsing
its "TxFrameRef" input pin "HIGH" for one nibble-period, coincident with the first nibble of a new "outbound" E3
FIGURE 214. AN ILLUSTRATION OF HOW TO INTERFACE THE "SYSTEM-SIDE TERMINAL EQUIPMENT" SIGNALS FOR
MODE 5 (NIBBLE-PARALLEL/LOCAL-TIMING/FRAME SLAVE) MODE OPERATION
System-Side Terminal
Equipment
XRT79L71 DS3/E3
Framer IC
E3_Data_Out[3:0]
E3_Nib_Clock_In
Tx_Start_of_Frame
TxNib[3:0]
TxNibClk
TxFrameRef
NibInt
VCC
4
34.368MHz Clock Source
TxInClk
8.592MHz
TxOH_Ind
E3_OH_Ind