![](http://datasheet.mmic.net.cn/Exar-Corporation/XRT79L71IB-F_datasheet_100145/XRT79L71IB-F_87.png)
PRELIMINARY
XRT79L71
72
REV. P2.0.0
1-CHANNEL DS3/E3 CLEAR-CHANNEL FRAMERLIU COMBO - CC/HDLC ARCHITECTURE
OPERATION OF THE TRANSMIT PAYLOAD DATA INPUT INTERFACE BLOCK
The Transmit Payload Data Input Interface block permits the user to configure it to operate in the following
combination of modes.
The Serial or Nibble-Parallel Interface Mode
The Loop-Timing or Local-Timing Mode
If the XRT79L71 is configured to operate in the Local-Timing Mode, then there are two additional sub-options.
The Frame-Master or Frame-Slave Mode
With these three sets of configuration options, the Transmit Payload Data Input Interface block can be
configured to operate in any one of the following six (6) Modes.
Mode 1 - Serial/Loop-Timing Mode
Mode 2 - Serial/Local-Timing/Frame Slave Mode
Mode 3 - Serial/Local-Timing/Frame Master Mode
Mode 4 - Nibble-Parallel/Loop-Timing Mode
Mode 5 - Nibble-Parallel/Local-Timing/Frame Slave Mode
Mode 6 - Nibble-Parallel/Local-Timing/Frame Master Mode
Table 8A presents a "Quick-Look" Summary of each of these Modes.
TxFrameRef
A11
I
Transmit DS3 Frame Reference Input:
The XRT79L71 permits the user to configure this input pin to function as the
Transmit DS3 Frame Generation Reference Input. Iinvoking this particular con-
figuration option, will cause the Transmit DS3 Framer block, within the
XRT79L71, to initiate DS3 frame generation anytime it detects a rising edge on
this input pin.
NOTE:
If tthis configuration option is implemented, it is imperative that this
particular input signal is synchronous with the TxInClk input signal.
Failure to do so will result in the transmission of erred DS3 frames to the
remote terminal equipment.
RxOutClk
B5
O
Loop-Timing Reference Clock Output Pin:
If the XRT79L71 is configured to operate in the Loop-Timing mode, then the
Transmit Section of the XRT79L71 will be configured to use the LIU Recovered
Clock signal as its timing source. In this case, the XRT79L71 will output a
44.736MHz clock signal via this particular output pin. In this configuration, the
TxInClk signal will be inactive and will NOT be used to sample and latch the data
on the TxSer input pin. In this case, the XRT79L71 will now be configured to
sample the TxSer input pin upon the rising edge of the RxOutClk signal.
NOTE:
This output pin will always be active, in the sense that it will always
generate a 44.736MHz clock signal, even when the XRT79L71 is NOT
configured to operate in the Loop-Timing Mode.
However, the
XRT79L71 will only use this particular clock signal to sample and latch
the data on the TxSer input pin whenever the XRT79L71 has been
configured to operate in the Loop-Timing Mode.
TABLE 13: LIST AND DESCRIPTION OF THE PINS ASSOCIATED WITH THE TRANSMIT PAYLOAD DATA INPUT INTERFACE
BLOCK
SIGNAL NAME
PIN/BALL #TYPE
DESCRIPTION