XRT74L73 Datasheet, PDF (205/488 Pages) Exar Corporation – 3 CHANNEL, ATM UNI/PPP DS3/E3 FRAMING CONTROLLER

PRELIMINARY
XRT74L73
3 CHANNEL, ATM UNI/PPP DS3/E3 FRAMING CONTROLLER
REV. P1.0.1
Method 1) in order to transmit a Yellow Alarm to
the remote terminal equipment.
In this example, the Terminal Equipment intends to in-
sert the appropriate overhead bits, into the Transmit
Overhead Data Input Interface, such that the
XRT74L73 will transmit a Yellow Alarm to the remote
terminal equipment. Recall that, for DS3 Applica-
tions, a Yellow Alarm is transmitted by setting both of
the X bits (within each outbound DS3 frame) to 0.
If one assumes that the connection between the Ter-
minal Equipment and the XRT74L73 are as illustrated
in Figure 64 then Figure 65 presents an illustration
of the signaling that must go on between the Terminal
Equipment and the XRT74L73.
FIGURE 65. ILLUSTRATION OF THE SIGNAL THAT MUST OCCUR BETWEEN THE TERMINAL EQUIPMENT AND THE
XRT74L73, IN ORDER TO CONFIGURE THE XRT74L73 TO TRANSMIT A YELLOW ALARM TO THE REMOTE TERMINAL
EQUIPMENT
Terminal Equipment/XRT72L5x Interface Signals
TxOHClk
TxOHFrame
TxOHIns
TxOH
0 0- 1
2
3
4
5
6
7
8 8-
X bit = 0
Remaining Overhead Bits with DS3 Frame
X bit = 0
TxOHFrame is sample “high”
Terminal Equipment asserts
“TxOHIns” and data on “TxOH” line
XRT72L5x device samples the TxOHIns and
TxOH signals.
TxOHFrame is sample “high”
Terminal Equipment asserts
“TxOHIns” and data on “TxOH” line
XRT72L5x device samples the TxOHIns and
TxOH signals.
In Figure 65 the Terminal Equipment samples the Tx-
OHFrame signal being "High" at the rising clock edge
# 0. At this point, the Terminal Equipment knows that
the XRT74L73 is just about to process the very first
overhead bit within a given outbound DS3 frame. Ad-
ditionally, according to Table 37 , the very first over-
head bit to be processed is the first X bit. In order to
facilitate the transmission of the Yellow Alarm, the
Terminal Equipment must set this X bit to 0. Hence,
the Terminal Equipment starts this process by imple-
menting the following steps concurrently.
a. Assert the TxOHIns input pin by setting it "High".
b. Set the TxOH input pin to 0.
After the Terminal Equipment has applied these sig-
nals, the XRT74L73 will sample the data on both the
TxOHIns and TxOH signals upon the very next falling
edge of TxOHClk (designated at 0- in Figure 65 .
Once the XRT74L73 has sampled this data, it will
then insert a "0" into the first X bit position, in the out-
bound DS3 frame.
Upon detection of the very next rising edge of the Tx-
OHClk clock signal (designated as clock edge 1 in
Figure 65 ), the Terminal Equipment will negate the
TxOHIns signal (e.g., toggles it "Low") and will cease
inserting data into the Transmit Overhead Data Input
Interface, until rising clock edge # 8 (of the TxOHClk
signal). According to Table 37 , rising clock edge # 8
indicates that the XRT74L73 is just about ready to
process the second X bit within the outbound DS3
frame. Once again, in order to facilitate the transmis-
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