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XRT79L71
PRELIMINARY
441
1-CHANNEL DS3/E3 CLEAR-CHANNEL FRAMERLIU COMBO - CC/HDLC ARCHITECTURE
REV. P2.0.0
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 208.
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 overhead bytes (in lieu of 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 FA1
and FA2 bytes), and it will do so for 8 consecutive bit-periods, when processing the remaining five (5) overhead
bytes. Therefore, for the E3, ITU-T G.832 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 the Transmit Payload Data Input Interface block is to be configured into the "Gapped Clock" Mode, then refer