AD9954 communication library

Overview

This library facilitates communication between the Arduino and Analog Devices AD9954 DDS chip.

Getting Started

You'll first need to include the SPI library, as well as this one. Then, you can declare an AD9954 object, like

#include <SPI.h>
#include <AD9954.h>
AD9954 DDS(ssPin, resetPin, updatePin, ps0, ps1, osk);

In your void setup(){ ... } function, you'll need to first start the SPI bus:

SPI.begin();
SPI.setClockDivider(4);
SPI.setDataMode(SPI_MODE0);
delay(500); // let things get set up...

(note, this is assuming you're using an Arduino Due...)

Then, initialize your DDS with a clock frequency:

DDS.initialize(400000000); // initialize DDS with 400 MHz clock

Currently implemented Features

I've currently implemented the basic single-tone mode, and the linear sweep mode.

Single-tone mode

After you've initialized the DDS, you can command it to output a particular frequency like

DDS.setFreq(25000000); // set DDS to 25 MHz

Linear sweep mode

You can also do a bi-directional linear sweep, using DDS.linearSweep(). The direction of the ramp is controlled by the PS0 pin, so PS0 HIGH will cause it to do a positive ramp (limited by a final frequency), and PS0 LOW will make it ramp down (limited by a lower-bound frequency). Eg,

// Function linearSweep -- places DDS in linear sweep mode.
//      Behavior is determined by two frequency tuning words, freq0 and freq1 (freq0 < freq1).
//      The PS0 pin HIGH will ramp towards freq1, PS0 LOW will ramp towards freq0.
//      The rate of the ramp is dictated by pos/negDF (positive/negative DeltaFreq), and pos/negRR (positive/negative RampRate).
//      
//      freq0: lower frequency bound (Hz)
//      freq1: upper frequency bound (Hz)
//      posDF: delta frequency for positive ramp (Hz)
//      negDF: delta frequency for negative ramp (Hz)
//      posRR: number between 0 and 255, indicating number of SYNC_CLK cycles spent at each
//              frequency value in the ramp. SYNC_CLK operates at 1/4 of the SYSCLK clock value. Typically SYNC_CLK = 100MHz.
//              Thus, the true "ramp rate" is, eg, posDF/(posRR*10 ns)
//      negRR: same as above, but for negative ramp.
//      
//      As a general rule, round up (not down) in calculating the delta frequency steps.
//
//      AD9954::linearSweep(freq0, freq1, posDF, posRR, negDF, negRR);

DDS.linearSweep(19500000, 20500000, 1, 1, 1, 1);

This would set the DDS for a linear sweep between 19.5 and 20.5 MHz, where the ramp rate is set at one SYNC_CLK cycle per frequency step (pos/negRR = 1), and 1 Hz between each frequency in the ramp (pos/negDF = 1). Thus, for a 400MHz clock, SYNC_CLK is 100 MHz (10ns per cycle) and so the ramp rate is

1 Hz/10 ns = 100 Hz per microsecond

Toggling the PS0 pin instructs the DDS which way to ramp; if it reaches the frequency bounds, it will hold that frequency until PS0 is toggled in the opposite direction.