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PRELIMINARY
XRT79L71
302
REV. P2.0.0
1-CHANNEL DS3/E3 CLEAR-CHANNEL FRAMERLIU COMBO - CC/HDLC ARCHITECTURE
CASE STUDY: The System-Side Terminal Equipment intends to insert the appropriate overhead bits
into the Transmit Overhead Data Input Interface using Method 2 in order to transmit the FERF/RDI
indicator to the remote terminal equipment.
For E3 ITU-T G.751applications, the FERF/RDI indication is transmitted by setting the A bit-field within f each
outbound E3 frame to "1".
If we were to assume that the connection between the System-Side Terminal Equipment and the Transmit
Overhead Data Input Interface block (of the XRT79L71) is as illustrated in Figure 141, then Figure 142 presents an illustration of the signaling that must go on between the System-Side Terminal Equipment and the
Transmit Overhead Data Input Interface when using Method 2.
In Figure 142, the System-Side Terminal Equipment samples the TxOHFrame and TxOHEnable output pins
being "High" during Falling Clock Edge # 0 within the TxInClk signal. At this point, the System-Side Terminal
Equipment know that the XRT79L71 is just about to process the very first overhead bit within a given outbound
E3 frame.
In order to facilitate the transmission of the FERF/RDI indicator, the System-Side Terminal
Equipment must set the "A" bit-field (within the outbound E3 frame) to "1". According to Table 41, the "A" bit-
field will be ready for processing coincident to the 10th assertion of the TxOHEnable output signal, following
the most recent assertion of TxOHFrame.
The System-Side Terminal Equipment can externally set the "A" bit-field (within each outbound E3 frame) to "1"
by implementing the following tasks in the sequence as depicted below.
TASK # 1 - Continuously sample both the TxOHFrame and the TxOHEnable output pins with each falling edge
of TxInClk. Whenever the System-Side Terminal Equipment samples both of these input pin "High", then it
should move on to TASK # 2.
FIGURE 142. 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 2)
TxInClk
TxOHFrame
TxOHEnable
TxOHIns
TxOH
System-Side Terminal Equipment
samples “TxOHFrame” and
“TxOHEnable” being “HIGH”
System-Side Terminal Equipment
responds by waiting for the “TxOHEnable” output
Pin to pulse 10 more times prior to asserting TxOHIns
and placing desired data on TxOH.
XRT79L71 device samples TxOH
here.
TxOHEnable Pulse # 10
A bit = 1
0
2
3
A
B
TxOHEnable Pulse # 0