
XRT79L71
PRELIMINARY
277
1-CHANNEL DS3/E3 CLEAR-CHANNEL FRAMERLIU COMBO - CC/HDLC ARCHITECTURE
REV. P2.0.0
If the XRT79L71 is configured to operate in Mode 3, then all of the following is true.
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 as its timing source.
Since the XRT79L71 is configured to operate in the Serial-Mode, it will sample and latch the data, being
applied to the TxSer input pin upon the rising edge of the TxInClk input signal.
The XRT79L71 will still pulse the TxFrame output pin coincident to whenever the Transmit Payload Data
Input Interface is processing the very last bit within a given E3 frame.
Figure 128 presents an illustration of how to Interface the System-Side Terminal Equipment to the Transmit
Payload Data Input Interface block of the XRT79L71 for Mode 3 operation.
Mode 3 Operation of the Transmit Payload Data Input Interface Block
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 34.386MHz clock signal at its E3_Clock_In input pin as depicted below in Figure 129.
The XRT79L71 will latch the contents of the TxSer input pin upon the rising edge of the TxInClk signal.
Finally, the XRT79L71 pulses its TxOH_Ind output pin "High" one bit-period prior to it 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.
FIGURE 128. AN ILLUSTRATION AS TO HOW SHOULD INTERFACE THE SYSTEM-SIDE TERMINAL EQUIPMENT SIGNALS
FOR
MODE 3 (SERIAL/LOCAL-TIMING/FRAME-SLAVE) MODE OPERATION
34.368 MHz
Clock Source
34.368 MHz
Clock Source
System-Side Terminal
Equipment
XRT79L71 DS3/E3
Framer IC
E3_Data_Out
E3_Clock_In
Tx_End_of_Frame
E3_Overhead_Ind
TxSer
TxInClk
TxFrame
TxOH_Ind
NibInt