XRT75R12IB datasheet(39/90 Pages) EXAR

39 / 90 page

XRT75R12

REV. 1.0.4

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 270

Ω

resistor and MRing_n pins to TRing_n lines via 270

Ω resistor as shown in Figure 24.

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 “Low” 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 “High” and when the transitions are detected again, DMO_n

toggles “Low”.

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 “High” and write a “1” to the TxON_n control bit. When the transmitter is turned off, TTIP_n and

TRing_n are tri-stated.

NOTES:

This feature provides support for Redundancy.

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 “1” to the TxON_n control bits transfers the control

to TxON pin.

FIGURE 24. TRANSMIT DRIVER MONITOR SET-UP.

TTIP(n)

TRing(n)

1:1

Ω

TxPOS(n)

TxNEG(n)

TxLineClk(n)

TPData(n)

TNData(n)

TxClk(n)

31.6

Ω + 1%

31.6

Ω +1%

MTIP(n)

MRing(n)

270

Ω

270

Ω

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