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PRELIMINARY
XRT79L71
438
REV. P2.0.0
1-CHANNEL DS3/E3 CLEAR-CHANNEL FRAMERLIU COMBO - CC/HDLC ARCHITECTURE
Mode 1 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 the
34.368MHz clock signal via the "RxOutClk" output signal.
NOTE: The "RxOutClk" signal is a buffered version of the "Recovered Line Clock" signal, from the Receive DS3/E3 LIU
Block).
This clock signal is used as the "System-Side Terminal Equipment" clock source by both the Transmit Payload
Data Input Interface block (of the XRT79L71) and the "System-Side Terminal Equipment" device or circuitry.
The "System-Side" Terminal Equipment should serially output the payload data (that is to be transported via
the "outbound" E3 data-stream) via its "E3_Data_Out" output pin. The user is advised to design the "System-
Side Terminal Equipment" circuitry such that it will update the data (via the "E3_Data_Out" output pin) upon the
rising edge of the 34.368MHz clock signal (at its "E3_Clock_In" input pin) as depicted below in Figure 207.
The XRT79L71 will latch the contents of the "TxSer" input pin, upon the rising edge of the "RxOutClk" signal.
The XRT79L71 will indicate that it is processing the very last bit of a given E3 frame by pulsing its "TxFrame"
output pin "HIGH" for one bit-period. The "TxFrame" output pin will have held "LOW" at all other times.
Whenever the System-Side Terminal Equipment detects this pulse at its "Tx_Start_of_Frame" input pin, then it
is expected to begin the transmission of the contents of the very next outbound E3 frame, via the
"E3_Data_Out" output (or the TxSer input) pin.
Finally, the Transmit Payload Data Input Interface block (within the XRT79L71) will indicate that it is about to
process an overhead bit by pulsing the "TxOH_Ind" output pin "HIGH" for one period prior to its processing. In
Figure 206, the "TxOH_Ind" output pin (of the XRT79L71) is connected to the "E3_Overhead_Ind" input pin of
the "System-Side Terminal Equipment" circuitry. Whenever the "E3_Overhead_Ind" input pin is pulsed "high"
the "System-Side" Terminal Equipment is expected to NOT transmit an E3 payload bit upon the very next rising
edge of "E3_Clock_In". Instead, the System-Side Terminal Equipment is expected to delay its transmission of
the very next payload bit by one "RxOutClk" clock period.
NOTES:
FIGURE 206. AN ILLUSTRATION OF HOW TO INTERFACE THE "SYSTEM-SIDE" TERMINAL EQUIPMENT TO THE
"TRANSMIT PAYLOAD DATA INPUT INTERFACE" BLOCK (OF THE XRT79L71) FOR MODE 1 (SERIAL/LOOP-TIMING)
OPERATION
System-Side Terminal
Equipment
XRT79L71 DS3/E3
Framer IC
E3_Data_Out
E3_Clock_In
Tx_End_of_Frame
E3_Overhead_Ind
TxSer
RxOutClk
TxFrame
TxOH_Ind
NibInt
34.368 MHz Clock Signal