![](http://datasheet.mmic.net.cn/Exar-Corporation/XRT79L71IB-F_datasheet_100145/XRT79L71IB-F_288.png)
XRT79L71
PRELIMINARY
273
1-CHANNEL DS3/E3 CLEAR-CHANNEL FRAMERLIU COMBO - CC/HDLC ARCHITECTURE
REV. P2.0.0
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 RxOutClk, 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 toperating the "Transmit Payload Data Input Interface" block in the "Gapped-Clock" Mode, refer to
Figure 125 presents an illustration of the Behavior of the System-Side Terminal Equipment/Transmit Payload
Data Input Interface signals for Mode 1 Operation.
Configuring the XRT79L71 to operate in Mode 1 (Serial/Loop-Timing)
The user can configure the XRT79L71 to operate in Mode 1 by executing the following steps.
STEP 1 - Design your board such that the System-Side Terminal Equipment circuitry interfaces to the
Transmit Payload Data Input Interface in the manner as depicted above inFigure 125. STEP 2 - Configure the XRT79L71 to operate in the Serial Mode
This can be accomplished by setting the NibIntf input pin to a logic "Low".
NOTE: This step also configures the Receive Payload Data Output Interface to operate in the Serial Mode.
STEP 3 - Configure the XRT79L71 to operate in the Loop-Timing Mode
This can be accomplished by setting Bits 1 and 0 (TimRefSel[1:0]) within the Framer Operating Mode Register
to [0, 0] as depicted below.
FIGURE 125. AN ILLUSTRATION OF THE BEHAVIOR OF THE SYSTEM-SIDE TERMINAL EQUIPMENT SIGNALS FOR MODE
1 (SERIAL/LOOP-TIMING) MODE OPERATION
System-Side Terminal Equipment Signals
E3_Clock_In
E3_Data_Out
Tx_End_of_Frame
E3_Overhead_Ind
XRT79L71 Transmit Payload Data Input Interface Block Signals
RxOutClk
TxSer
TxFrame
TxOH_Ind
Payload[1522]
Payload[1523]
FAS, Bit 1
FAS, Bit 2
Payload[1522]
Payload[1523]
FAS, Bit 1
FAS, Bit 2
Note: The FAS Bits will not be processed by the
Transmit Payload Data Input Interface.
E3 Frame Number N
E3 Frame Number N + 1
Note: TxFrame pulses high to denote
E3 Frame Boundary.
Note: TxOH_Ind pulses high for
12 bit periods in order to
denote Overhead Data
(e.g., the FAS, A and N bits).