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PRELIMINARY
XRT79L71
106
REV. P2.0.0
1-CHANNEL DS3/E3 CLEAR-CHANNEL FRAMERLIU COMBO - CC/HDLC ARCHITECTURE
NOTES:
1.
The shaded rows designate those Overhead bits that the XRT79L71 will permit the user to insert into the
outbound DS3 data-streamvia the Transmit Overhead Data Input Interface block.
2.
The un-shaded rows designate those Overhead bits that the XRT79L71 CANNOT insert into the outbound DS3
data-stream.
TASK # 3: After the System-Side Terminal Equipment has waited the appropriate number of clock edges from
the TxOHFrame signal being sampled "High", it should assert the TxOHIns input signal by pulling 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 very next falling
edge of the TxOHClk output signal.
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 the next rising edge of TxOHClk is detected. Afterwards, the System-Side
Terminal Equipment should toggle the TxOHIns input pin "Low" and wait until another appropriate TxOHClk
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 1 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
Overhead Data Input Interface block of the XRT79L71 is as illustrated in Figure 44, then Figure 45 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 1.
FIGURE 45. 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 1)
System-Side Terminal Equipment/XRT79L71 Transmit Overhead Data Input Interface Signals
TxOHClk
TxOHIns
TxOHFrame
TxOH
Remaining Overhead Bits with DS3 Frame
X bit = 0
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 8 rising edges of TxOHClk, the
System-Side Terminal Equipment asserts
The “TxOHIns” and places data on the
“TxOH” line”
XRT79L71 device samples the “TxOHIns” and
“TxOH” input signals upon falling edge of
TxOHClk.
0+ 0- 1
2
3
4
5
6
7
8+ 8-