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XRT79L71
PRELIMINARY
111
1-CHANNEL DS3/E3 CLEAR-CHANNEL FRAMERLIU COMBO - CC/HDLC ARCHITECTURE
REV. P2.0.0
it "High". Concurrently, the System-Side Terminal Equipment should also place the appropriate value of the
overhead bit to be inserted into the outbound DS3 data-stream onto the TxOH input signal. The Transmit
Overhead Data Input Interface block will sample and latch the data residing on the TxOH input pin upon the
second rising edge of TxInClk after TxOHEnable was sampled "High".
TASK # 4: The System-Side Terminal Equipment should hold the TxOHIns input pin "High" and also hold the
value of the TxOH signal stable until TxOHEnable is sampled at a logic "high" level again. Afterwards, the
System-Side Terminal Equipment should toggle the TxOHIns input pin "Low" and wait until another appropriate
TxOHEnable pulsing period comes up, for inserting an overhead bit into the outbound DS3 data-stream.
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 (Far-End-Receive
Failure) indicator to the remote terminal equipment.
For DS3 applications, the FERF indication is transmitted by setting both the X bits within each outbound DS3
frame to "0".
If we were to assume that the connection between the System-Side Terminal Equipment and the Transmit
Overheads Data Input Interface block of the XRT79L71 is as illustrated in Figure 46, then Figure 47 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 47 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 knows that the XRT79L71 is just about to process the very first overhead bit within a given
outbound DS3 frame. According to Table 21, the very first overhead bit to be processed within a given DS3
frame is the first X bit. In order to facilitate the transmission of the FERF indicator, the System-Side Terminal
FIGURE 47. 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 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 asserting TxOHIns
and placing desired data on TxOH.
XRT79L71 device samples TxOH
here.
TxOHEnable Pulse # 8
X bit = 0
0
2
3
A
B