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PRELIMINARY
XRT79L71
444
REV. P2.0.0
1-CHANNEL DS3/E3 CLEAR-CHANNEL FRAMERLIU COMBO - CC/HDLC ARCHITECTURE
1.
Since the E3, ITU-T G.832 Frame consists of overhead bytes (in lieu of overhead bits), whenever the "TxOH_Ind"
output pin (of the XRT79L71) pulses "high" it will do so for 16 consecutive bit-periods (when processing the FA1
and FA2 bytes), and it will do so for 8 consecutive bit-periods, when processing the remaining five (5) overhead
bytes.
Therefore, for the E3, ITU-T G.832 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.
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.
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.
4.ITo operate the Transmit Payload Data Input Interface block in the "Gapped-Clock" Mode, Refer to
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 210. 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".
STEP 3 - Configure the XRT79L71 to operate in the Local-Timing/Frame Master Mode
FIGURE 211. 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[4238]
Payload[4239]
FA1, Bit 7
FA1, Bit 6
Payload[4238]
Payload[4239]
FA1, Bit 7
FA1, Bit 6
Note: The FA1 byte 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
16-bit periods in order to
denote Overhead Data
(e.g., the FA1 and FA2 bytes).