//SPI example using AD7373 DAC from Analog Devices
//set DAC for simultaneous update of two channels
//
//connect MOSI B.5 to DIN on AD7373
//connect SCLK B.7 to SCLK on AD7373
//connect B.4 to notSYNC on the AD7373

#include <mega32.h>
#include <spi.h> // SPI driver routine

#define begin {
#define end }

unsigned char junk, Aout, DACctlOne, DACctlTwo;
unsigned char DDSacc, DDSinc;

void main(void)
begin

    //set up SPI control register SPCR
    //bit 7 SPIE=0 no ISR
    //bit 6 SPE=1 enable spi
    //bit 5 DORD=0 msb first 
    //bit 4 MSTR=1 Mega32 is spi master
    //bit 3 CPLO=1 clock polarity
    //bit 2 CPHA=1 clock phase
    //bit 1,0 rate sel=00 along with SPSR.0=1 sets clk to f/2 = 8 MHz
    SPCR = 0b01011100 ;                                                                               
    SPSR = 1; 
    
    //set up i/o data direction
    DDRB.4 = 1; //output chip select for ADC
    DDRB.5 = 1; //output MOSI 
    //DDRB.6 = 0; //input MISO is not used by the DAC
    DDRB.7 = 1; //output SCLK    
    
    DDSinc = 16; //sawtooth rate
    
    //DAC control word
    // bit 7 notINT/EXT set to notINT = 0. Use internal Vref
    // bit 6 = 0
    // bit 5 LDAC = 0 load and update both channels when set
    // bit 4 PDB = 0 pwer down channel B
    // bit 3 PDA = 0 pwer down channel A
    // bit 2 notA/B = 0 chooses A
    // bit 1 CR1=0  control bits modify load mode
    // bit 0 CR0=1  set to load A from SR
    // Load A from shift register
    DACctlOne = 0b00000001 ; 
    // Load B from SR and and update both outputs
    DACctlTwo = 0b00100100 ;
    
    while (1)
    begin 
        PORTB.4 = 0;            //SYNC low begins load      
        SPDR = DACctlOne;       //set DAC parameters 
        while (SPSR.7==0) ;
        SPDR = DDSacc ;         //send channel A
        while (SPSR.7==0) ;
        PORTB.4 = 1;            //SYNC high ends load  
        
        PORTB.4 = 0;            //SYNC low begins load   
        SPDR = DACctlTwo;       //set DAC parameters  
        while (SPSR.7==0) ;
        SPDR = DDSacc+64 ;      //send channel B
        while (SPSR.7==0) ;
        PORTB.4 = 1;            //SYNC high ends load  
         
        DDSacc = DDSacc + DDSinc;  // sawtooth generator    
    end
end