daWandlerDirekt.c

/**************************************************************************

% Projekt 9   : Ansteuerung DA-Converter MCP4921

% Autor       : 

% Filename    : daWandler.c

% Startdate   : 22.02.14

% Enddate     : 01.03.14

% Version     : 1.0

%**************************************************************************

%

%Auf ATMEGA16 16MHZ   ext. Cristal

%

%**************************************************************************

%

%Test zum Ansteueren des DA-Converters MCP4921. 

%

%**************************************************************************/

#include <avr/interrupt.h>    

#include <avr/io.h>  

#define UC_CS    PB4

#define UC_MOSI   PB5

#define UC_MISO   PB6

#define UC_SCK    PB7

typedef union ushort {                       

      uint16_t Short;                          

      uint8_t Byte[2];

} ushort;

volatile uint8_t flg = 0;

//prototypen

  unsigned char spi_transfer(unsigned char);

  void update();

  void init();

int main() {

  init();

  while(1){

  if (flg == 1){    

      cli();

      update();

      flg = 0;

      sei();

    }

  }

  return 0;

}

//Updates den MCP4921 

void update() {

  ushort value;

  value.Short = 4000;

  //value.Short *= amplitude;

  //Definiere die Kontroll-Werte fuer den chip

  //  bit 15 0 = Write to DAC register

  //  bit 14 0 = Unbuffered

  //  bit 13 0 = Output gain select (X2)

  //  bit 12 1 = Output shutdown control (Active mode) 

  value.Short |= 0x1000;

  //Output the data

  PORTB &= ~_BV(UC_CS);

  spi_transfer(value.Byte[1]);

  spi_transfer(value.Byte[0]);

  PORTB |= _BV(UC_CS);

}

// Transfers 1 byte of data via SPI

unsigned char spi_transfer(unsigned char data)

{

  SPDR = data;

  while (!(SPSR & (1<<SPIF)))     // warte bis uebertragen 

  {

  };

  return SPDR;                    // return the received byte

  }

void init() 

{

  //Init Ports

  DDRB  |= (1<<UC_MOSI) | (1<<UC_SCK) | (1<<UC_CS);

  PORTB = _BV(UC_CS);

  //Init SPI

  SPCR = (1<<SPE) | (1<<MSTR);        //Enable SPI, Master, set clock rated fclk/4

  SPSR = (1<<SPI2X);

  //Set up Timer2

  TCCR2 |=  (1<<WGM21);  //>ocr2 comp.

  TCCR2 =   _BV(CS21);//>prescale 8

  OCR2 = 10;

  TIMSK |= (1<<OCIE2);

  sei();  

}

ISR(TIMER2_COMP_vect) {

  flg = 1;

}