Diff: main.cpp

Revision:

0:21d4a8e3d6be

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/main.cpp	Sat Oct 26 18:22:46 2013 +0000
@@ -0,0 +1,91 @@
+// MBED driver for AD9851 digital synthesizer using hacked SPI interface
+// Original code for AD9850 by Liam Goudge Sept 2013
+// Modified for AD9851 and KL25Z by Mike Richards Oct 2013
+
+#include "mbed.h"
+
+
+SPI device (PTD2, PTD3, PTD1); // Set the KL25Z SPI pins
+DigitalOut CS(PTD0); // Use pin PTD0 as a fake Chip select (AD9851's FQ_UD line)
+DigitalOut ADReset(PTA13); // Use Pin PTA13 as the reset line for AD9851
+int targetFrq; // 32-bit frequency word for the AD9851
+int phase; // Phase and multiplier word for AD9851
+
+Serial pc(USBTX, USBRX); // tx, rx for debug terminal
+
+int reverseBits (int source)
+{
+// 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
+    int mask=0;;
+    int i=0;
+    int target=0;
+    int bitTarget=0x80000000; // Hard-wired for 32-bit inversion
+
+    for (i=0;i<32;i++) { // ditto
+        mask=1<<i;   
+        bitTarget=1<<(31-i); // ditto
+
+        if (source & mask)
+            target=target | bitTarget;
+    } 
+    return target;
+}    
+     
+void writeSPI(int frq, int phase)
+{           
+// Send the 40-bit packet. NB: KL25Z only supports 8-bit SPI so send five 8-bit packets
+    
+    device.format(8,0); // 8-bits per packet, mode 0 (CPOL=0 CPHA=0)
+    device.frequency(1000000); //SPI clock set to 1MHz
+
+    wait_ms(1);
+
+    // 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
+    CS=1; // assert chip select (a.k.a FQ_UD frequency update input to AD9851)
+    wait_ms(1);
+    CS=0;
+    
+    // Write 5 x 8-bit packets for the frequency word  
+    device.write(frq>>24); // Packet 1
+    device.write(frq>>16); // Packet 2
+    device.write(frq>>8);  // Packet 3
+    device.write(frq);     // Packet 4
+    device.write(phase);   // Packet 5 - Finish with the phase, multiplier and factory settings byte
+
+    // Now pulse FQ_UD again to load the word into the DDS
+    CS=0;
+    wait_ms(1);
+    CS=1;
+    wait_ms(1);
+    CS=0;
+}
+    
+
+int main()
+{
+    
+    
+    int DesFrq = 5000000; // Set the desired output frequency in Hz
+    float Mult = 23.86093; // Multiplier for boards using a 30MHz clock oscillator and 6x multiplier
+    targetFrq= DesFrq * Mult ; // targetFrq is the 32-bit frequency word for the AD9851
+    phase = 0x80; // Set the 6x clock multiplier for systems with 30MHz reference oscillator.
+    
+    // Reset the AD9851. Active high logic. Minimum reset period 5 clock cycles
+    ADReset=0;
+    wait_ms(5);
+    ADReset=1;
+    wait_ms(5);
+    ADReset=0;
+        
+    
+    while(1)
+    {
+    
+    writeSPI(reverseBits(targetFrq),phase); // Transfer the frequency settings to the AD9851
+   
+   
+    
+    }      
+        
+        
+}
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