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____________________________________________________ DS34T101, DS34T102, DS34T104, DS34T108
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10.13.2 LIU Transmitter
The LIU is configured for E1 or T1/J1 mode by setting the
LTRCR.T1J1E1S bit appropriately.
10.13.2.1 Waveshaping
The LIU transmitter uses a sequencer and a precision digital-to-analog converter (DAC) to create the waveforms
that are transmitted onto the outbound cable. The waveforms meet the latest ANSI, ETSI, ITU and Telcordia
generated, along with the line build out field in
LTISR.L[2:0], if applicable. Due to the nature of its design, the
transmitter adds very little jitter (less than 0.005UIP-P broadband from 10Hz to 100kHz) to the transmit signal. Also,
the waveforms created are independent of the duty cycle of TCLK.
10.13.2.2 Line Build-Out
The transmitter line driver can handle both CEPT 30/ISDN-PRI lines for E1 and long-haul (CSU) or short-haul
(DSX-1) lines for T1. The L[2:0] field in
LTISR specifies the line build-out for E1 and T1.
10.13.2.3 Line Driver Enable/Disable
are put in a high-impedance state. When the
TXENABLE pin is high and
LMCR.TXEN=1, the line driver is enabled.
10.13.2.4 Interfacing to the Line
The transmitter is transformer-coupled to the line. Typically, the transmitter interfaces to the outgoing coaxial cable
or twisted-pair wiring through a 1:2 step-up transformer.
Figure 10-68 shows the arrangement of the transformer
with respect to the TTIP and TRING pins. The transmitter termination is always internal. Set
LTISR.TIMPOFF=0
of the transformer.
10.13.2.5 AIS Generation
When
LMCR.TAIS = 1, the LIU transmitter generates AIS (unframed all ones) using E1CLK or T1CLK from CLAD1
as the timing reference. In addition, when
LMCR.ATAIS = 1, the transmitter generates AIS when the LIU receiver
indicates loss of signal (LOS).
10.13.2.6 Short-Circuit Detector
The LIU transmitter has an automatic short-circuit detector that activates when the short-circuit resistance is
approximately 25
or less.
LRSR.SCS provides a real-time indication of when the short-circuit limit has been
exceeded. Latched status bits
LLSR.SCD and SCC are set when
LRSR.SCS changes state from low-to-high and
high-to-low, respectively. These latched status bits can cause an interrupt request if enabled by the corresponding
bits in
LSIMR. The short-circuit detector is disabled for CSU modes (i.e., when
LTISR.L[2:0] = 101, 110, or 111).
10.13.2.7 Open-Circuit Detector
The LIU transmitter can also detect when
TTIP and
TRING are open circuited.
LRSR.OCS provides a real-time
indication of when the open-circuit limit has been exceeded. Latched status bits
LLSR.OCD and OCC are set when
LRSR.OCS changes state from low-to-high and high-to-low, respectively. These latched status bits can cause an
interrupt request if enabled by the corresponding bits in
LSIMR. The open-circuit detector is disabled for CSU
modes (i.e., when
LTISR.L[2:0] = 101, 110, or 111).
10.13.2.8 Transmitter Power-Down
The transmitter can be powered down to reduce power consumption by setting
LMCR.TPDE=1. When the
transmitter is powered down,
TTIP and
TRING are high impedance.