XRT73L03 Datasheet, PDF (52/62 Pages) Exar Corporation – 3 CHANNEL E3/DS3/STS-1 LINE INTERFCE UNIT

XRT73L03 3 CHANNEL E3/DS3/STS-1 LINE INTERFACE UNIT
REV. P1.0.13
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PRELIMINARY
Shut off the Channel(n) Transmit Driver by toggling
the TxOFF(n) input pin (pin 88, 87 or 86) "High". Turn
on the Transmit Driver by toggling the TxOFF(n) input
pin "Low".
b. Operating in the HOST Mode
Turn off the Channel(n) Transmit Driver by setting the
TxOFF(n) bit-field in 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)
Writing a "0" into this bit-field enables the Channel(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 XRT73L03 was designed such that
either Transmitter can quickly be turned-on or turned-off by
toggling the TxOFF(n) 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 XRT73L03.
1
X
X
X
X
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
HIGH
0
OFF (Transmitter is Tri-Stated)
OFF (Transmitter is Tri-Stated)
HIGH
1
OFF (Transmitter is Tri-Stated)
To control the state of each transmitter via the Micro-
processor Serial interface, connect the TxOFF(n) in-
put pins 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 XRT73L03 or another LIU.
Activate the Channel(n) Transmit Drive Monitor by
connecting the MTIP(n) pin (pin 117, 94 or 105) to the
TTIP(n) line through a 270 Ohm resistor connected in
series, and connecting the MRing(n) pin (pin 116, 95
or 104) to the TRing(n) line through a 270 Ohm resis-
tor connected in series. Such an approach is illustrat-
ed in Figure 32.
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