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XRT79L71
PRELIMINARY
285
1-CHANNEL DS3/E3 CLEAR-CHANNEL FRAMERLIU COMBO - CC/HDLC ARCHITECTURE
REV. P2.0.0
The user can configure the XRT79L71 to operate in Mode 5 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 133. STEP 2 - Configure the XRT79L71 to operate in the Nibble-Parallel Mode
This can be accomplished by setting the NibIntf input pin to a logic "High".
STEP 3 - Configure the XRT79L71 to operate in the Local-Timing/Frame Slave Mode
This can be accomplished by setting Bits 1 and 0 (TimRefSel[1:0]) within the Framer Operating Mode Register
to [0, 1] as depicted below.
5.2.1.6
Mode 6 - Nibble-Parallel/Local-Timing/Frame Master Mode Operation for the Transmit
Payload Data Input Interface Block
If the XRT79L71 is configured to operate in Mode 6 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.
In this mode, the XRT79L71 will use the TxInClk signal to derive the TxNibClk signal.
For E3 Applications, the TxNibClk frequency is exactly one-fourth of the TxInClk clock signal or 8.592MHz.
Since the XRT79L71 is configured to operate in the Nibble-Parallel Mode, it will sample and latch the data,
being applied to the TxNib[3:0] input pin upon the third rising edge of TxInClk input clock signal, following a
given rising edge of the TxNibClk output clock signal.
The XRT79L71 will pulse the TxNibFrame output pin coincident to whenever the Transmit Payload Data
Input Interface is processing the very last bit within a given E3 frame.
Figure 134 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 6 operation.
Framer Operating Mode Register (Address = 0x1100)
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
Local Loop
Back
IsDS3
Internal LOS
Enable
RESET
Direct
Mapped
ATM
Frame For-
mat
TimRefSel[1:0]
R/W
0
1
0
1
0
1