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XRT75R12_15 Datasheet, PDF (39/90 Pages) Exar Corporation – TWELVE CHANNEL E3/DS3/STS-1 LINE INTERFACE UNIT WITH JITTER | |||
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XRT75R12
REV. 1.0.5
TWELVE CHANNEL E3/DS3/STS-1 LINE INTERFACE UNIT WITH JITTER ATTENUATOR
4.6 Transmit Drive Monitor
This feature is used for monitoring the transmit line for occurrence of fault conditions such as a short circuit on
the line or a defective line driver. To activate this function, connect MTIP_n pins to the TTIP_n lines via a 270ïï
resistor and MRing_n pins to TRing_n lines via 270ï resistor as shown in Figure 24.
FIGURE 24. TRANSMIT DRIVER MONITOR SET-UP.
TxPOS(n)
TxNEG(n)
TxLineClk(n)
TTIP(n)
TRing(n)
TPData(n)
TNData(n)
TxClk(n)
MTIP(n)
MRing(n)
R1
31.6ï +1%
R2
31.6ï + 1% 1:1
R3
75ï
R1
270ï
R2
270ï
When the MTIP_n and MRing_n are connected to the TTIP_n and TRing_n lines, the drive monitor circuit
monitors the line for transitions. The DMO_n (Drive Monitor Output) will be asserted âLowâ as long as the
transitions on the line are detected via MTIP_n and MRing_n. If no transitions on the line are detected for 128
± 32 TxClk_n periods, the DMO_n output toggles âHighâ and when the transitions are detected again, DMO_n
toggles âLowâ.
NOTE: The Drive Monitor Circuit is only for diagnostic purpose and does not have to be used to operate the transmitter.
4.7 Transmitter Section On/Off
The transmitter section of each channel can either be turned on or off. To turn on the transmitter, set the input
pin TxON to âHighâ and write a â1â to the TxON_n control bit. When the transmitter is turned off, TTIP_n and
TRing_n are tri-stated.
NOTES:
1. This feature provides support for Redundancy.
2. If the XRT75R12 is configured in Host mode, to permit a system designed for redundancy to quickly shut-off the
defective line card and turn on the back-up line card, writing a â1â to the TxON_n control bits transfers the control
to TxON pin.
36
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