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XRT79L71
PRELIMINARY
465
1-CHANNEL DS3/E3 CLEAR-CHANNEL FRAMERLIU COMBO - CC/HDLC ARCHITECTURE
REV. P2.0.0
In Figure 222, the System-Side Terminal Equipment samples the TxOHFrame signal being "High" during
Rising Edge Clock Edge # 0 with the TxOHClk signal. At this point, the System-Side Terminal Equipment
knows that the XRT79L71 is just about to process the very first overhead bit within a given E3 frame.
According to Table 60, the FERF/RDI bit will be processed at TxOHClk clock edge # 32. In order to facilitate
the transmission of the FERF/RDI indicator, the System-Side Terminal Equipment must (1) wait for 32
TxOHClk clock periods, and (2) then set this particular bit-field to "1".
Once the System-Side Terminal
Equipment has waited through the 32 TxOHClk clock periods, it sets the FERF/RDI 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 FERF/RDI bit-position within the outbound
E3 frame.
Upon detection of the very next rising edge of the TxOHClk clock signal (designated as Clock Edge # 33, in
Figure 222), 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.
6.2.2.2
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.
FIGURE 222. ILLUSTRATION OF THE SIGNALING THAT MUST OCCUR BETWEEN THE SYSTEM-SIDE TERMINAL EQUIP-
MENT AND THE
TRANSMIT OVERHEAD DATA INPUT INTERFACE OF THE XRT79L71, IN ORDER TO CONFIGURE THE
XRT79L71 TO TRANSMIT THE FERF/RDI INDICATOR TO THE REMOTE TERMINAL EQUIPMENT (USING METHOD 1)
System-Side Terminal Equipment/XRT79L71 Transmit Overhead Data Input Interface Signals
TxOHClk
TxOHIns
TxOHFrame
TxOH
Remaining Overhead Bits within the E3 Frame
FERF = 1
TxOHFrame is sample “high”
System-Side Terminal Equipment
Asserts “TxOHIns” and data on
“TxOH” line.
XRT79L71 device samples the “TxOHIns and
TxOH input signals upon falling of TxOHClk
After 34 rising edges of TxOHClk, the
System-Side Terminal Equipment asserts
The “TxOHIns” and places data on the
“TxOH” line”
0
1 - - -31
32
33
34
35
36
37