XRT72L50 Datasheet, PDF (170/471 Pages) Exar Corporation – SINGLE CHANNEL DS3/E3 FRAMER IC WITH HDLC CONTROLLER

XRT72L50
SINGLE CHANNEL DS3/E3 FRAMER WITH HDLC CONTROLLER
REV. 1.2.1
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FIGURE 46. 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
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 samples the TxOHIns and
TxOH signals.
Terminal Equipment asserts
“TxOHIns” and data on “TxOH” line
XRT72L5x samples the TxOHIns and
TxOH signals.
In Figure 46 the Terminal Equipment samples the TxOHFrame signal being "High" at the rising clock edge #0.
At this point, the Terminal Equipment knows that the XRT72L50 is just about to process the very first overhead
bit within a given outbound DS3 frame. The very first overhead bit in Table 18 to be processed is the first X bit.
To facilitate the transmission of the Yellow Alarm, the Terminal Equipment must set this X bit to “0”. 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 “0”.
After the Terminal Equipment has applied these signals, the XRT72L50 samples the data on both the TxOHIns
and TxOH signals upon the very next falling edge of TxOHClk (designated at 0- in Figure 46). Once the
XRT72L50 has sampled this data, it then inserts a "0" into the first X bit position in the outbound DS3 frame.
Upon detection of the very next rising edge of the TxOHClk clock signal (designated as clock edge 1 in
Figure 46), the Terminal Equipment negates the TxOHIns signal (e.g., toggles it "Low") and ceases inserting
data into the Transmit Overhead Data Input Interface until rising clock edge #8 of the TxOHClk signal. In
Table 18 the rising clock edge #8 indicates that the XRT72L50 is just about ready to process the second X bit
within the outbound DS3 frame. To facilitate the transmission of the Yellow Alarm, this X Bit must also be set to
“0”. The Terminal Equipment implements the following steps concurrently.
a. Assert the TxOHIns input pin by setting it "High".
b. Set the TxOH input to “0”.
After the Terminal Equipment has applied these signals, the XRT72L50 samples the data on both the TxOHIns
and TxOH signal upon the very next falling edge of TxOHClk (designated as 8- in Figure 46). Once the
XRT72L50 has sampled this data, it inserts a "0" into the second X bit position in the outbound DS3 frame.
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