Programmable Modulus Window - Analog Devices AD9915 User Manual

Evaluation Board
User Guide
Use the Rising Step Size and Falling Step Size checkboxes to
set the step size of the rising or falling ramp. The unit for these
changes depending on what type of ramp is being generated.
The Rising Sweep Ramp Rate and Falling Sweep Ramp
Rate are used to set the time between each rising or falling step
on the ramp. This is in units of microseconds.
The No Dwell High and No Dwell Low boxes set the
corresponding bit functions in the register map. Use the Up,
Down, and Pause buttons at the bottom of the window to
control the direction or to hold the ramp. The Ramp Finished
indicator turns on when the ramp is complete.

PROGRAMMABLE MODULUS WINDOW

Figure 13. Programmable Modulus Window
The chip is in programmable modulus mode when the Enable
Programmable Modulus check box is selected. The digital
ramp generator mode will automatically be disabled.
The Programmable Modulus window is used to alter the
frequency equation of the DDS core, making it possible to
implement fractions that are not restricted to a power of 2 in the
denominator.
When you enter the desired output frequency (in terms of
MHz) in the Fout box, the values in the Register Values boxes
and the Divide Ratio boxes are automatically updated. You can
also directly input a divide ratio, which in this case will
automatically update the Register Values boxes and the
Output Frequency box.
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