XRT73LC00A_08 Datasheet, PDF (52/63 Pages) Exar Corporation – E3/DS3/STS-1 LINE INTERFACE UNIT

REV. 1.0.1
XRT73LC00A
E3/DS3/STS-1 LINE INTERFACE UNIT
Shut off the Transmit Driver by toggling the TXOFF input pin (pin 35) “High”. Turn on the Transmit Driver by
toggling the TXOFF input pin “Low”.
When the XRT73LC00A is operating in the HOST Mode
If the XRT73LC00A is operating in the HOST Mode, the TXOFF input pin is disabled. Consequently,
theTransmit Driver is turned off by writing to Command Register CR1 and setting the TXOFF bit-field (bit D4) to
“1”.
COMMAND REGISTER CR1 (ADDRESS = 0X01)
D4
D3
D2
D1
D0
TXOFF TAOS TXCLKINV TXLEV TXBIN
1
X
X
X
X
NOTE: If the Transmitter is shut off via the TXOFF feature, the XRT73LC00A can NOT be configured to operate in the
Analog Local Loop-Back Mode. To perform diagnostics on the chip and still invoke the TXOFF feature as in
System Redundancy Applications, use the Digital Local Loop-Back feature instead.
4.5 The Transmit Drive Monitor Features
The Transmit Drive Monitor feature performs monitoring of the line in the Transmit Direction for the occurrence
of fault conditions such as a short circuit on the line or a defective Transmit Drive in the XRT73LC00A.
The Transmit Drive Monitor is activated by connecting the MTIP pin (pin 44) to the TTIP line through a 270 Ω
resistor connected in series and by connecting the MRING pin (pin 43) to the TRING line through a 270 Ω
resistor connected in series, as illustrated in Figure 30.
FIGURE 30. THE XRT73LC00A EMPLOYING THE TRANSMIT DRIVE MONITOR FEATURES
TTIP
TRING
T1
R1 = 31.6 Ω
R2 = 31.6 Ω
1:1
R5 = 75Ω
MTIP
R3 = 270 Ω
MRING
R4 = 270 Ω
When the Transmit Drive Monitor circuitry is connected to the line as illustrated in Figure 26, then it monitors
the line for transitions. As long as the Transmit Drive Monitor circuitry detects transitions on the line via the
MTIP and MRING pins, it keeps the DMO (Drive Monitor Output) signal “Low”. However, if the Transmit Drive
Monitor circuit detects no transitions on the line for 128±32 TCLK periods, then the DMO signal toggles “High”.
NOTES:
1. The Transmit Drive Monitor circuit does not have to be used to operate the Transmit Section of the XRT73LC00A.
This is purely a diagnostic feature.
2. The Transmit Drive Monitor feature can also be used to monitor the Transmit Output Line Signal of another LIU IC
as illustrated in Figure 31.
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