XRT73L03A Datasheet, PDF (53/62 Pages) Exar Corporation – 3 CHANNEL DS3/E3/STS-1 LINE INTERFACE UNIT

XRT73L03A
3 CHANNEL DS3/E3/STS-1 LINE INTERFACE UNIT
REV. 2.0.4
4.4 TXOFF FEATURES
The Transmit Section of each Channel in the
XRT73L03A can be shut off. When this feature is in-
voked, the Transmit Section of the configured channel
is shut-off and the Transmit Output signals (e.g.,
TTIP_(n) and TRing_(n)) is tri-stated. This feature is
useful for system redundancy conditions or during di-
agnostic testing.
a. Operating in the Hardware Mode
Shut off the Transmit Driver concurrently within all
Channels by toggling the TxOFF input pin “High".
Turn on the Transmit Driver by toggling the TxOFF in-
put pin “Low".
b. Operating in the HOST Mode
Turn off the Transmit Driver within Channel(n) by set-
ting the TxOFF_(n) bit-field within Command Register
CR1-(n) to "1".
COMMAND REGISTER CR1-(n)
D4
D3
D2
D1
D0
TxOFF_(n) TAOS_(n) TxClkINV_(n) TxLEV_(n) TxBIN_(n)
1
X
X
X
X
Writing a "0" into this bit-field enables the Chan-
nel(n)Transmit Driver.
NOTE: In order to permit a system designed for redundancy
to quickly shut-off a defective line card and turn-on the
back-up line card, the XRT73L03A was designed such that
either Transmitter can quickly be turned-on or turned-off by
toggling the TxOFF input pins. This approach is much
quicker then setting the TxOFF_(n) bit-fields via the Micro-
processor Serial Interface.
Table 6 presents a Truth Table which relates the set-
ting of the TxOFF external pin and bit-field for a chan-
nel to the state of the Transmitter. This table applies
to all Channels of the XRT73L03A.
TABLE 6: THE RELATIONSHIP BETWEEN THE TXOFF INPUT PIN, THE TXOFF BIT FIELD AND THE STATE OF THE
TRANSMITTER
STATE OF THE TXOFF
INPUT PIN
STATE OF THE TXOFF
BIT FIELD
STATE OF THE TRANSMITTER
LOW
0
ON (Transmitter is Active)
LOW
1
OFF (Transmitter is Tri-Stated)
HIGH
0
OFF (Transmitter is Tri-Stated)
HIGH
1
OFF (Transmitter is Tri-Stated)
To control the state of all transmitters via the Micro-
processor Serial interface, connect the TxOFF input
pin to GND.
4.5 THE TRANSMIT DRIVE MONITOR FEATURES
The Transmit Drive Monitor is used to monitor the line
in the Transmit Direction for the occurrence of fault
conditions such as a short circuit on the line, a defec-
tive Transmit Drive in the XRT73L03A or another LIU.
Activate the Channel(n) Transmit Drive Monitor by
connecting the MTIP_(n) pin to the TTIP_(n) line
through a 270 Ohm resistor connected in series, and
connecting the MRing_(n) pin to the TRing_(n) line
through a 270 Ohm resistor connected in series.
Such an approach is illustrated in Figure 37.
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