main.cpp

00001 // MBED driver for AD9851 digital synthesizer using hacked SPI interface
00002 // Original code for AD9850 by Liam Goudge Sept 2013
00003 // Modified for AD9851 and KL25Z by Mike Richards Oct 2013
00004 
00005 #include "mbed.h"
00006 
00007 
00008 SPI device (PTD2, PTD3, PTD1); // Set the KL25Z SPI pins
00009 DigitalOut CS(PTD0); // Use pin PTD0 as a fake Chip select (AD9851's FQ_UD line)
00010 DigitalOut ADReset(PTA13); // Use Pin PTA13 as the reset line for AD9851
00011 int targetFrq; // 32-bit frequency word for the AD9851
00012 int phase; // Phase and multiplier word for AD9851
00013 
00014 Serial pc(USBTX, USBRX); // tx, rx for debug terminal
00015 
00016 int reverseBits (int source)
00017 {
00018 // Unfortunately need to invert bit order of the desired frequency setting since MBED only allows for MSB first from SPI. We need LSB first for AD9851
00019     int mask=0;;
00020     int i=0;
00021     int target=0;
00022     int bitTarget=0x80000000; // Hard-wired for 32-bit inversion
00023 
00024     for (i=0;i<32;i++) { // ditto
00025         mask=1<<i;   
00026         bitTarget=1<<(31-i); // ditto
00027 
00028         if (source & mask)
00029             target=target | bitTarget;
00030     } 
00031     return target;
00032 }    
00033      
00034 void writeSPI(int frq, int phase)
00035 {           
00036 // Send the 40-bit packet. NB: KL25Z only supports 8-bit SPI so send five 8-bit packets
00037     
00038     device.format(8,0); // 8-bits per packet, mode 0 (CPOL=0 CPHA=0)
00039     device.frequency(1000000); //SPI clock set to 1MHz
00040 
00041     wait_ms(1);
00042 
00043     // First do chip select. Need to use a GPIO to fake the chip select since MBED doesn't allow to set positive logic CS signal
00044     CS=1; // assert chip select (a.k.a FQ_UD frequency update input to AD9851)
00045     wait_ms(1);
00046     CS=0;
00047     
00048     // Write 5 x 8-bit packets for the frequency word  
00049     device.write(frq>>24); // Packet 1
00050     device.write(frq>>16); // Packet 2
00051     device.write(frq>>8);  // Packet 3
00052     device.write(frq);     // Packet 4
00053     device.write(phase);   // Packet 5 - Finish with the phase, multiplier and factory settings byte
00054 
00055     // Now pulse FQ_UD again to load the word into the DDS
00056     CS=0;
00057     wait_ms(1);
00058     CS=1;
00059     wait_ms(1);
00060     CS=0;
00061 }
00062     
00063 
00064 int main()
00065 {
00066     
00067     
00068     int DesFrq = 5000000; // Set the desired output frequency in Hz
00069     float Mult = 23.86093; // Multiplier for boards using a 30MHz clock oscillator and 6x multiplier
00070     targetFrq= DesFrq * Mult ; // targetFrq is the 32-bit frequency word for the AD9851
00071     phase = 0x80; // Set the 6x clock multiplier for systems with 30MHz reference oscillator.
00072     
00073     // Reset the AD9851. Active high logic. Minimum reset period 5 clock cycles
00074     ADReset=0;
00075     wait_ms(5);
00076     ADReset=1;
00077     wait_ms(5);
00078     ADReset=0;
00079         
00080     
00081     while(1)
00082     {
00083     
00084     writeSPI(reverseBits(targetFrq),phase); // Transfer the frequency settings to the AD9851
00085    
00086    
00087     
00088     }      
00089         
00090         
00091 }