XRT7300IV View Datasheet(PDF) - Exar Corporation
Part Name
Description
MFG CO.
'XRT7300IV' PDF : 55 Pages View PDF
XRT7300
E3/DS3/STS-1 LINE INTERFACE UNIT
REV. 1.1.1
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4.4 TXOFF FEATURES
The XRT7300 allows the Transmit Driver in the Trans-
mit Section of the chip to be shut off. This feature can
be advantageous for system redundancy conditions
or during diagnostic testing. This feature can be acti-
vated by either of the following ways.
When the XRT7300 is operating in the Hardware
Mode
Shut off the Transmit Driver by toggling the TXOFF in-
put pin (pin 35) “High”. Turn on the Transmit Driver by
toggling the TXOFF input pin “Low”.
When the XRT7300 is operating in the HOST
Mode
If the XRT7300 is operating in the HOST Mode, the
TXOFF input pin is disabled. Consequently, the-
Transmit Driver is turned off by writing to Command
Register CR1 and setting the TXOFF bit-field (bit D4)
to “1”.
NOTE: If the Transmitter is shut off via the TXOFF feature,
the XRT7300 can NOT be configured to operate in the Ana-
log 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 monitor-
ing of the line in the Transmit Direction for the occur-
rence of fault conditions such as a short circuit on the
line or a defective Transmit Drive in the XRT7300.
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 31.
COMMAND REGISTER CR1 (ADDRESS = 0X01)
D4
D3
D2
D1
D0
TXOFF TAOS TXCLKINV TXLEV TXBIN
1
X
X
X
X
FIGURE 31. THE XRT7300 EMPLOYING THE TRANSMIT DRIVE MONITOR FEATURES
TTIP
TRING
T1
R1 = 36 Ω
R2 = 36 Ω
1:1
R5 = 75Ω
MTIP
R3 = 270 Ω
MRING
R4 = 270 Ω
When the Transmit Drive Monitor circuitry is connect-
ed to the line as illustrated in Figure 26, then it moni-
tors 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
XRT7300. This is purely a diagnostic feature.
40
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