Datasheet

____________________________________________________ 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
specifications (see Figure 10-69 and Figure 10-70). The
LTRCR.T1J1E1S field specifies the waveform to be
generated, along with the line build out field in LTISR.L[2:0], if appli
cable. Due to the nature of its design, the
transmitter adds very little jitter (less than 0.005UI
P-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 spe
cifies the line build-out for E1 and T1.
10.13.2.3 Line Driver Enable/Disable
When the TXENABLE pin is low or when LMCR.TXEN=0, the transmitter line driver is disabled, and TTIP/TRING
are put in a high-impedance state. When the TXENABLE pin is hig
h 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
and set LTISR.TIMPL[1:0] to sp
ecify the termination impedance. Table 10-60 specifies the required characteristics
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.AT
AIS = 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 provid
es a real-time indication of when the short-circuit limit has been
exceeded. Latched status bits LLSR.SCD and S
CC 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 sho
rt-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.O
CD 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 ope
n-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 a
re high impedance.