XRT72L50 Datasheet, PDF (277/471 Pages) Exar Corporation – SINGLE CHANNEL DS3/E3 FRAMER IC WITH HDLC CONTROLLER

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XRT72L50
SINGLE CHANNEL DS3/E3 FRAMER WITH HDLC CONTROLLER
REV. 1.2.1
FIGURE 102. ILLUSTRATION OF THE SIGNAL THAT MUST OCCUR BETWEEN THE TERMINAL EQUIPMENT AND THE
XRT72L50 IN ORDER TO CONFIGURE THE XRT72L50 TO TRANSMIT A YELLOW ALARM TO THE REMOTE TERMINAL
EQUIPMENT
Terminal Equipment/XRT72L5x Interface Signals
0
1
4
5
6
7
8
9
10 10-
TxOHClk
TxOHFrame
TxOHIns
TxOH
Remaining Overhead Bits with E3 Frame
A bit = 1
TxOHFrame is sampled “High”
Terminal Equipment asserts TxOHIns and
Data on TxOH line.
XRT72L5x Framer device samples TxOH and
TxOHIns signals
In Figure 102 the Terminal Equipment samples the TxOHFrame signal being "High" at rising clock edge # 0.
From this point, the Terminal Equipment will wait until it has detected the 10th rising edge of the TxOHClk
signal. At this point, the Terminal Equipment knows that the XRT72L50 is just about to process the A bit within
a given outbound E3 frame. Additionally, according to Table 46, the 10th overhead bit to be processed is the
"A" bit. In order to facilitate the transmission of the Yellow Alarm, the Terminal Equipment must set this "A" bit
to "1". Hence, the Terminal Equipment starts this process by implementing the following steps concurrently.
a. Assert the TxOHIns input pin by setting it "High".
b. Set the TxOH input pin to "1".
After the Terminal Equipment has applied these signals, the XRT72L50 will sample the data on both the
TxOHIns and TxOH signals upon the very next falling edge of TxOHClk (designated as "10-" in Figure 102).
Once the XRT72L50 has sampled this data, it will then insert a "1" into the "A" bit position, in the outbound E3
frame.
Upon detection of the very next rising edge of the TxOHClk clock signal (designated as clock edge 1 in
Figure 102, 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.
After the Terminal Equipment has performed this insertion procedure, it leaves the remaining overhead bits
(within this particular outbound E3 frame) in-tact, by terminating this Overhead Bit Insertion procedure. The
Terminal Equipment should now terminate this overhead bit insertion, by doing the following.
a. Assert the TxOHIns input pin by setting it "High".
b. Set the TxOH input to "0".
If the Terminal Equipment wishes to continue its transmission of the Yellow Alarm condition to the Remote
Terminal Equipment, then it should resume the Overhead Bit Insertion procedure (as described above), at the
beginning of each outbound E3 frame (or each time TxOHFrame is sampled "High”).
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