XRT73L03 Datasheet, PDF (35/62 Pages) Exar Corporation – 3 CHANNEL E3/DS3/STS-1 LINE INTERFCE UNIT

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PRELIMINARY
3 CHANNEL E3/DS3/STS-1 LINE INTERFACE UNIT XRT73L03
REV. P1.0.13
COMMAND REGISTER CR1-(N)
D4
D3
D2
D1
D0
TxOFF(n)
TAOS(n)
TxClkINV(n)
TxLEV(n)
TxBin(n)
0
X
X
1
X
2.4.3 Design Guideline for Setting the Transmit
Line Build-Out Circuit
The TxLEV(n) input pins or bit-fields should be set
based upon the overall cable length between the
Transmitting Terminal and the Digital Cross Connect
system where the pulse template measurements are
made.
If the cable length between the Transmitting Ter-
minal and the DSX-3 or STSX-1 is less than 225
feet, enable the Transmit Line Build-Out circuit by
setting the TxLEV(n) input pin or bit-field to "0".
NOTE: In this case, the configured channel outputs shaped
(e.g., not square-wave) pulses onto the line via its TTIP(n)
and TRing(n) output pins. The shape of this output pulse is
such that it complies with the pulse template requirements
even when subjected to cable loss ranging from 0 to 225
feet.
If the cable length between the Transmitting Ter-
minal and the DSX-3 or STSX-1 is greater than 225
feet, disable the Transmit Line Build-Out circuit by
setting the TxLEV(n) input pin or bit-field to "1".
NOTE: In this case, the configured channel in the
XRT73L03 outputs partially-shaped pulses onto the line via
the TTIP(n) and TRing(n) output pins. The cable loss that
these pulses experience over long cable lengths (e.g.,
greater than 225 feet) causes these pulses to be properly
shaped and comply with the appropriate pulse template
requirement.
2.4.4 The Transmit Line Build-Out Circuit and
E3 Applications
The ITU-T G.703 Pulse Template Requirements for
E3 states that the E3 transmit output pulse should be
measured at the Secondary Side of the Transmit Out-
put Transformer for Pulse Template compliance. In
other words, there is no Digital Cross Connect Sys-
tem pulse template requirement for E3. Consequent-
ly, the Transmit Line Build-Out circuit in a given Chan-
nel in the XRT73L03 is disabled whenever that chan-
nel has been configured to operate in the E3 Mode.
2.5 INTERFACING THE TRANSMIT SECTIONS OF THE
XRT73L03 TO THE LINE
The E3, DS3 and SONET STS-1 specification docu-
ments all state that line signals transmitted over coax-
ial cable are to be terminated with 75 Ohm resistor.
Interface the Transmit Section of the XRT73L03 in
the manner illustrated in Figure 16 to accomplish this.
FIGURE 16. RECOMMENDED SCHEMATIC FOR INTERFACING THE TRANSMIT SECTION OF THE XRT73L03 TO
THE LINE
TxPOS(n)
TxNEG(n)
TxLineClk(n)
TTIP(n)
Channel (n)
TPData(n)
TNData(n)
TxClk(n)
TRing(n)
R1
31.6 Ω
R2
31.6 Ω
Only One Channel Shown
J1
BNC
1:1
32