
XRT79L71
PRELIMINARY
79
1-CHANNEL DS3/E3 CLEAR-CHANNEL FRAMERLIU COMBO - CC/HDLC ARCHITECTURE
REV. P2.0.0
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 DS3 frame.
Figure 34 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
44.736MHz clock signal to both the System-Side Terminal Equipment circuitry and the XRT79L71. More
specifically, this 44.736MHz clock signal will be applied to both the DS3_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 DS3 data-stream via its DS3_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 DS3_Data_Out output pin upon the rising
edge of the 44.736MHz clock signal at its DS3_Clock_In input pin as depicted below in Figure 35.
The XRT79L71 will latch the contents of the TxSer input pin upon the rising edge of the TxInClk signal. The
XRT79L71 will indicate that it is processing the very last bit of a given DS3 frame by pulsing its TxFrame output
pin "High" for one bit-period. The TxFrame output pin will be held "Low" at all other times. Whenever the
System-Side Terminal Equipment detects this pulse at its Tx_End_of_Frame input pin, then it is expected to
begin the transmission of a contents of the very next outbound DS3 frame, via the DS3_Data_Out output or the
TxSer input pin.
NOTES:
FIGURE 34. AN ILLUSTRATION OF HOW TO INTERFACE THE SYSTEM-SIDE TERMINAL EQUIPMENT SIGNALS FOR MODE
3 (SERIAL/LOCAL-TIMING/FRAME-SLAVE) MODE OPERATION
44.736MHz
Clock Source
44.736MHz
Clock Source
System-Side Terminal
Equipment
XRT79L71 DS3/E3
Framer IC
DS3_Data_Out
DS3_Clock_In
Tx_Start_of_Frame
DS3_Overhead_Ind
TxSer
TxInClk
TxFrame
TxOH_Ind
NibInt