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PRELIMINARY
XRT79L71
278
REV. P2.0.0
1-CHANNEL DS3/E3 CLEAR-CHANNEL FRAMERLIU COMBO - CC/HDLC ARCHITECTURE
NOTES:
1.
Since the E3, ITU-T G.751 Frame consists of 12 consecutive overhead bits, whenever the TxOH_Ind output pin of
the XRT79L71 pulses "High" it will do so for 12 consecutive bit-periods when processing the FAS, A and and N
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 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.
In this particular mode, the Transmit Direction circuitry (within the XRT 79L71) is dictating the instant that it will
initiate the generation of a new E3 frame; and is referred to as the "Frame Master". As a consequence, this
particular mode is referred to as the "Frame Master" Mode.
3.
In contrast to "Mode 2" operation, if the XRT 79L71 is configured to operate in "Mode 3", then it is NOT imperative
that the "TxFrameRef" input be synchronized to the "TxInClk" input clock signal. In this case, we recommend that
the user tie the "TxFrameRef" input pin to GND.
4.
If operating the Transmit Payload Data Input Interface block in the "Gapped-Clock" Mode, trefer to
Figure 129 presents an illustration of the behavior of the System-Side Terminal Equipment/Transmit Payload
Data Input Interface signals for Mode 3 Operation.
Configuring the XRT79L71 to operate in Mode 3 (Serial/Local-Timing/Frame-Master Mode)
The user can configure the XRT79L71 to operate in Mode 3 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 in Figure 129. 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".
FIGURE 129. AN ILLUSTRATION OF THE BEHAVIOR OF THE SYSTEM-SIDE TERMINAL EQUIPMENT SIGNALS FOR MODE
3 (SERIAL/LOCAL-TIMING/FRAME-MASTER) 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 Signals
TxInClk
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).