![](http://datasheet.mmic.net.cn/Exar-Corporation/XRT79L71IB-F_datasheet_100145/XRT79L71IB-F_314.png)
XRT79L71
PRELIMINARY
299
1-CHANNEL DS3/E3 CLEAR-CHANNEL FRAMERLIU COMBO - CC/HDLC ARCHITECTURE
REV. P2.0.0
waited through the 10 TxOHClk clock periods, it sets the "A" bit-field to "1" by implementing the following two
tasks concurrently.
TASK 1 - The System Side Terminal Equipment asserts the TxOHIns input pin by setting it "High".
TASK 2 - The System-Side Terminal Equipment sets the TxOH input pin to "1".
After the System-Side Terminal Equipment has executed these two tasks, the XRT79L71 will sample both the
TxOHIns and the TxOH input pins being "High" during the very next falling edge of TxOHClk. Once the
XRT79L71 has sampled these two signals, it will insert a "1" into the "A" bit-position within the outbound E3
frame.
Upon detection of the very next rising edge of the TxOHClk clock signal (designated as Clock Edge # 11, in
Figure 140), the System-Side Terminal Equipment will negate (or de-assert) the TxOHIns input signal (e.g.,
toggle it "Low") and cease inserting data into the Transmit Overhead Data Input Interface for the remainder of
this particular E3 frame period. Afterwards, the System-Side Terminal Equipment will repeat all of the steps
that have been outlined in this case study.
5.2.2.2
Operating the Transmit Overhead Data Input Interface block using Method 2 - The TxInClk/
TxOHEnable Method
This particular method is referred to as the TxInClk/TxOHEnable method for the following reasons.
a. The System-Side Terminal Equipment will use the TxOHEnable output pin (from the Transmit Overhead
Data Input Interface block) to keep track of which overhead bit is being processed by the Transmit
Overhead Data Input Interface block at any given time.
b. The Transmit Overhead Data Input Interface block will use the rising edge of TxInClk in order to sample
and latch the data residing on the TxOH input pin.
If Method 2 is used, the System-Side Terminal Equipment will need to interface to the following Transmit
Overhead Data Input Interface pins.
TxOH
TxOHFrame
TxInClk
TxOHEnable
TxOHIns
If Method 2 is used then the users system must be designed such that the System-Side Terminal Equipment
will be interfaced to the Transmit Overhead Data Input Interface block, in a manner as presented below in