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Transmit clock input. TPOS and TNEG are sampled on the falling
edge of TCLK. If TCLK is grounded, the output drivers enter a high-Z state, except
during Remote Loopback.
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Input for positive pulse to be transmitted on the twisted-pair
line.
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Input for negative pulse to be transmitted on the twisted-pair
line.
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status. Setting MODE Low puts the LXT300Z in the Hardware (H/W) mode. In the
Hardware Mode, the serial interface is disabled and hard-wired pins are used to control
configuration and report status.
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Received data outputs. A signal on
RNEG corresponds to receipt of a negative pulse on RTIP and RRING. A signal on
RPOS corresponds to receipt of a positive pulse on RTIP and RRING. RNEG and
RPOS outputs are Non-Return-to-Zero (NRZ). Both outputs are stable and valid on the
rising edge of RCLK.
LXT300Z only: In the Host Mode, CLKE determines the clock edge at which these out-
puts are stable and valid. In the Hardware Mode both outputs are stable and valid on
the rising edge of RCLK.
5HFRYHUHG &ORFNï
This is the clock recovered from the signal received at RTIP and
RRING.
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An external crystal operating at four
times the bit rate (6.176 MHz for DSX-1, 8.192 MHz for E1 applications with an 18.7
pF load) is required to enable the jitter attenuation function of the LXT300Z. These
pins may also be used to disable the jitter attenuator by connecting the XTALIN pin to
the positive supply through a resistor, and floating the XTALOUT pin.
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DPM goes High when the transmit monitor loop
(MTIP and MRING) does not detect a signal for 63 ±2 clock periods. DPM remains
High until a signal is detected.
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LOS goes High when 175 consecutive spaces have been detected.
LOS returns Low when a mark is detected.
7UDQVPLW 7LSâ 7UDQVPLW 5LQJï
Differential Driver Outputs. These outputs are
designed to drive a 25
Ω
load. The transmitter will drive 100
Ω
shielded twisted-pair
cable through a 1:2 step-up transformer without additional components. To drive
75
Ω
coaxial cable, two 2.2
Ω
resistors are required in series with the transformer.
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The AMI signal received from the line is applied at these
pins. A center-tapped, center-grounded, 2:1 step-up transformer is required on these
pins. Data and clock from the signal applied at these pins are recovered and output on
the RPOS/RNEG and RCLK pins.
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This
LXT300Z Host Mode
output goes Low to flag the host
processor when LOS or DPM go active. INT is an open-drain output and should be tied
to power supply RV+ through a resistor. INT is reset by clearing the respective register
bit (LOS and/or DPM).
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The signal applied at this pin in the
LXT300Z Hard-
ware Mode and LXT301Z
is used in conjunction with EC2 and EC3 inputs to determine
shape and amplitude of AMI output transmit pulses.
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The serial data input stream is applied to this pin when the
LXT300Z
operates in the
Host Mode.
SDI is sampled on the rising edge of SCLK.
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The signal applied at this pin in the
LXT300Z Hard-
ware Mode and LXT301Z
is used in conjunction with EC1 and EC3 inputs to determine
shape and amplitude of AMI output transmit pulses.
6HULDO 'DWD 2XW
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The serial data from the on-chip register is output on
this pin in the
LXT300Z Host Mode.
If CLKE is High, SDO is valid on the rising edge
of SCLK. If CLKE is Low SDO is valid on the falling edge of SCLK. This pin goes to
a high-impedance state when the serial port is being written to and when CS is High.
(TXDOL]HU &RQWURO ê
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The signal applied at this pin in the
LXT300Z Hard-
ware Mode and LXT301Z
is used in conjunction with EC1 and EC2 inputs to determine
shape and amplitude of AMI output transmit pulses.
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This input is used to access the serial interface in the
LXT300Z Host Mode.
For each read or write operation, CS must transition from High
to Low, and remain Low.
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This input controls loopback functions in the
LXT300Z Hardware Mode and LXT301Z.
Setting RLOOP High enables the Remote
Loopback mode. Setting both RLOOP and LLOOP High causes a Reset.
6HULDO &ORFN
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This clock is used in the
LXT300Z Host Mode
to write data
to or read data from the serial interface registers.
/RFDO /RRSEDFN
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This input controls loopback functions in the
LXT300Z
Hardware Mode and LXT301Z.
Setting LLOOP High enables the Local Loopback
Mode.
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Setting CLKE High causes RPOS and RNEG to be valid on
the falling edge of RCLK, and SDO to be valid on the rising edge of SCLK. When
CLKE is Low, RPOS and RNEG are valid on the rising edge of RCLK, and SDO is
valid on the falling edge of SCLK.
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When High, TAOS causes the
LXT300Z (Hardware
Mode) and LXT301Z
to transmit a continuous stream of marks at the TCLK frequency.
Activating TAOS causes TPOS and TNEG inputs to be ignored. TAOS is inhibited dur-
ing Remote Loopback.
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decoupling circuitry. Isolation between the transmit and
receive circuits is provided internally.
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The LXT300Z and LXT301Z are fully integrated PCM
transceivers for both 1.544 Mbps (DSX-1) and 2.048
Mbps (E1) applications. Both transceivers allow full-
duplex transmission of digital data over existing twisted-
pair installations. The first page of this data sheet shows a
simplified block diagram of the LXT300Z; Figure 2
shows the LXT301Z. The LXT301Z is similar to the
LXT300Z, but does not incorporate the Jitter Attenuator
and associated Elastic Store, or the serial interface port.
The LXT300Z and LXT301Z transceivers each interface
with two twisted-pair lines (one twisted-pair for transmit,
one twisted-pair for receive) through standard pulse trans-
formers and appropriate resistors.
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Upon power up, the transceiver is held static until the
power supply reaches approximately 3 V. Upon crossing
this threshold, the device begins a 32 ms reset cycle to cal-
ibrate the transmit and receive delay lines and lock the
Phase Lock Loop to the receive line. A reference clock is
required to calibrate the delay lines. The transmitter refer-
ence is provided by TCLK. MCLK provides the receiver
reference for the LXT301Z. The crystal oscillator pro-
vides the receiver reference in the LXT300Z. If the
LXT300Z crystal oscillator is grounded, MCLK is used as
the receiver reference clock.
The transceiver can also be reset from the Host or Hard-
ware Mode. In Host Mode, reset is commanded by simul-
taneously writing RLOOP and LLOOP to the register. In
Hardware Mode, reset is commanded by holding RLOOP
and LLOOP High simultaneously for 200 ns. Reset is ini-
tiated on the falling edge of the reset request. In either
mode, reset clears and sets all registers to 0 and then begins
calibration.
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The LXT300Z and LXT301Z are low-power CMOS
devices. Each operates from a single +5 V power supply
which can be connected externally to both the transmitter
and receiver. However, the two inputs must be within ± .3V
of each other, and decoupled to their respective grounds
separately. Refer to Application Information for typical
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