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XRT79L71
PRELIMINARY
275
1-CHANNEL DS3/E3 CLEAR-CHANNEL FRAMERLIU COMBO - CC/HDLC ARCHITECTURE
REV. P2.0.0
Whenever the XRT79L71 has been configured to operate in this mode, then one is required to supply a
34.368MHz clock signal to both the System-Side Terminal Equipment circuitry and the XRT79L71. More
specifically, this 34.368MHz clock signal will be applied to both the E3_Clock_In input of the System-Side
Terminal Equipment and the TxInClk input pin of the XRT79L71, in parallel.
The System-Side Terminal Equipment will 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 127.
The XRT79L71 will latch the contents of the TxSer input pin, upon the rising edge of the TxInClk 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 bit-period, coincident
with the first bit a new outbound E3 frame being applied to the TxSer input pin. Once the XRT79L71 detects
the rising edge of the input at its TxFrameRef input pin, it will begin to generate and transmit a new E3 frame.
NOTES:
1.
In this particular mode, the System-Side Terminal Equipment is controlling the start of Frame Generation and is
referred to as the Frame Master. Since the XRT79L71 does not control or dictate the instant that it will generate a
new E3 frame, but is dictated by the System-Side Terminal Equipment it is referred to as the Frame Slave.
2.
It the XRT79L71 is configured to operate in the Mode 2 then it is imperative that the Tx_Start_of_Frame or
TxFrameRef signal is synchronized to the TxInClk input clock signal.
If the user fails to insure that the
TxFrameRef input signal is synchronized to the "TxInClk" input clock signal, then the XRT 79L71 will transmit
erred E3 data to the remote terminal equipment.
Finally, the XRT79L71 pulses its TxOHInd output pin "High" one bit-period prior to its processing a given
overhead bit within the outbound E3 frame. Since the TxOH_Ind output pin of the XRT79L71 is electrically
connected to the E3_Overhead_Ind input pin of the System-Side Terminal Equipment, whenever the
XRT79L71 pulses its TxOH_Ind output pin "High", it will also drive the E3_Overhead_Ind input pin of the
System-Side Terminal Equipment "High". Whenever the System-Side Terminal Equipment detects this pin
toggling "High" it should delay transmission of the very next E3 payload bit by one TxInClk clock period.
NOTES:
1.
Since the E3, ITU-T G.832 Frame consists of 12 consecutive overhead bits, whenever the TxOH_Ind output pin of
the XRT79L71 pulses "High" it will do so for 16 consecutive bit-periods when processing the FAS, A and N bits.
Therefore, for the E3, ITU-T G.751 framing format, whenever the System-Side Terminal Equipment detects the
TxOH_Ind output pin being pulled "High", it is expected to (1) continuously sample the state of the TxOH_Ind
output pin with each rising edge of TxInClk and (2) to NOT transmit an E3 payload bit to the Transmit Payload
Data Input Interface block until it samples the TxOH_Ind output pin toggling "Low".
2.
2.If configuring the Transmit Payload Data Input Interface block in the "Gapped Clock" Mode, trefer to
SectionFigure 127 presents an illustration of the behavior of the System-Side Terminal Equipment/Transmit Payload
Data Input Interface signals for Mode 2 Operation.