XRT79L71
PRELIMINARY
443
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.
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 211.
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.
NOTES:
FIGURE 210. AN ILLUSTRATION AS TO HOW SHOULD INTERFACE THE "SYSTEM-SIDE TERMINAL EQUIPMENT" SIG-
NALS 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