AN3619| Application Note
Maxim/Dallas > App Notes > TELECOM Keywords: T1, E1, Transmit Pulse, Template
Aug 30, 2005
APPLICATION NOTE 3619
DS26334 and DS26324 Transmit Pulse Control
The DS26334 and DS26324 line interface units (LIUs) contain precise methods for making minor or major changes to the output pulse. This application note provides the information required to access factory test registers that allow the transmit waveform to be modified to meet a wide variety of application requirements. With the addition of network-protection components and/or the need to route signals through connectors and other PCB requirements, it is sometimes necessary to manipulate the transmit waveform.
T1 and E1 Transmit Waveform Programmable Sections
The DS26334 and DS26324 contain registers that provide control for the transmit pulse in two major areas, amplitude and timing. T1 and E1 transmit pulses are divided into sections, each of which can be manipulated to provide the desired waveform. Figure 1 shows how the T1 pulse is divided and the registers that control each section. Figure 2 provides the same information for the E1 pulse.
T1 and E1 Transmit Waveform Amplitude Control
The amplitude of the DS26334 and DS26324 transmit pulse can be controlled in two ways. 1. Adjusting the DAC gain The LITXLAE register bits DAC[3:0] provide positive and negative adjustment of all the T1 or E1 levels simultaneously. 2. Partial waveform level adjustment The WLA[3:0] bits of the level adjustment registers provide fine-tuning of specific sections of the waveform. The step size of the voltage level will change in proportion to the programmed DAC gain. If the DAC gain is increased by 10%, the step sizes will also increase by 10%.
T1 and E1 Transmit Waveform Timing Control
The timing of the DS26334 and DS26324 transmit pulse levels are controlled by the CEA[2:0] bits of the level adjustment registers. Each edge can be moved in both positive and negative directions in increments of 1/32 of TCLK.
General Recommendations
Modifying the DAC gain is the easiest method of controlling the amplitude of the transmit pulse because it will control the entire waveform with only one register change. Using the DAC gain first will allow for minimal (if any) modifications of the individual level adjustment registers. The maximum output of the DAC will be affected by VDD. At lower levels of VDD, the maximum DAC gain setting might be unattainable. Changing VDD will also affect the maximum voltage attainable by the line driver's output
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