XRT75L04 Datasheet, PDF (30/57 Pages) Exar Corporation – FOUR CHANNEL E3/DS3/STS-1 LINE INTERFACE UNIT WITH JITTER

XRT75L04
FOUR CHANNEL E3/DS3/STS-1 LINE INTERFACE UNIT WITH JITTER ATTENUATOR
REV. 1.0.4
The Pulse Shaper Block also includes a Transmit Build Out Circuit, which can either be disabled or enabled by
setting the TxLEV_n input pin “High” or “Low” (in Hardware Mode) or setting the TxLEV_n bit to “1” or “0” in the
control register (in Host Mode).
For DS3/STS-1 rates, the Transmit Build Out Circuit is used to shape the transmit waveform that ensures that
transmit pulse template requirements are met at the Cross-Connect system. The distance between the
transmitter output and the Cross-Connect system can be between 0 to 450 feet.
For E3 rate, since the output pulse template is measured at the secondary of the transformer and since there is
no Cross-Connect system pulse template requirements, the Transmit Build Out Circuit is always disabled.
4.3.1 Guidelines for using Transmit Build Out Circuit:
If the distance between the transmitter and the DSX3 or STSX-1, Cross-Connect system, is less than 225 feet,
enable the Transmit Build Out Circuit by setting the TxLEV_n input pin “Low” (in Hardware Mode) or setting the
TxLEV_n control bit to “0” (in Host Mode).
If the distance between the transmitter and the DSX3 or STSX-1 is greater than 225 feet, disable the Transmit
Build Out Circuit.
4.3.2 Interfacing to the line:
The differential line driver increases the transmit waveform to appropriate level and drives into the 75Ω load as
shown in Figure 6.
4.4 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 16.
FIGURE 16. TRANSMIT DRIVER MONITOR SET-UP.
TTIP(n)
R1
31.6Ω +1%
TxPOS(n)
TxNEG(n)
TxLineClk(n)
TPOS(n)
TNEG(n)
TxCLK(n)_TRING(n)
RxB
MTIP(n)
R4 270Ω
RxA
MRING(n)
R5 270Ω
XRT75L04 (0nly one channel shown)
R2
31.6Ω + 1%
R3
75Ω
1:1
Case 1:
MTIP_1 connected to TTIP_1
MRING_1 connected to TRING_1
TxMON_1 (bit) = 0
As shown in the figure 18, connect MTIP_1 to TTIP_1 and MRING_1 to TRING_1 via the 270 Ω resistors.
When no transitions on the line are detected for 128 ± 32 TxClk_1 periods, the DMO_1 pin will toggle “High”.
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