adc.c

#include <avr/io.h>

// Mega16 Pinout

#define MOSI  4

#define MISO  6

#define SCLK  7

#define SS    4

unsigned int get_adc(unsigned char adata)

{

  static unsigned int temp=0;

  PORTB &= ~(1<<SS);                  // set cs on low to activied the adc

                                      // maybe here a little delay

  SPDR = adata;                        // put the data into send register

  while(!(SPSR & (1<<SPIF)));          // send 1 Byte over HW SPI and wait for tx complete int  

  temp = SPDR;                        // put the received data to a static temp variable

  temp = temp << 8;                    // shift the temp variable 8 steps left

  SPDR = adata;                        // put the data into send register

  while(!(SPSR & (1<<SPIF)));          // send 1 Byte over HW SPI and wait for tx complete int    

  temp |= SPDR;                        // put the received data to a static temp variable

  PORTB |= (1<<SS);                    // set cs on high to disable the adc

  return temp;                        // return the adc value

}

void spim_init(void)

{

  // SET the Ports to output 

  DDRB |= (1<<MOSI) | (1<<SCLK) | (1<<SS);

  // SET MISO to input

  DDRB &= ~(1<<MISO); 

  // SPI Enable, SPI Master, SPI CLK XTAL/16, LSB First

  SPCR |= (1<<SPE)|(1<<MSTR)|(1<<SPR0);    

  PORTB |= (1<<SS);    // CS High because the SPI ADC is low active

}

int main (void)

{

  static unsigned int adc_value=0;  // uint variable

  spim_init();                       // Init HW SPI Master

  adc_value = get_adc(0xFF);        // Get data from SPI ADC send anything to generate the clock

  for(;;){}

}