adc.c

atmega8的片内A/D转换操作

//ICC-AVR application builder : 2005-3-1 22:02:29
// Target : M8
// Crystal: 8.0000Mhz

#include <iom8v.h>
#include <macros.h>
#include <74164.h>

unsigned char    display[4];  // 显示缓冲区
unsigned char    dis;         // 当前显示
unsigned int     adc;          // 保存AD转换的值
unsigned char    time;        // AD转换的时间间隔


//TIMER0 initialisation - prescale:256
// WGM: Normal
// desired value: 5mSec
// actual value:  4.992mSec (0.2%)
void timer0_init(void)
{
 TCCR0 = 0x00; //stop
 TCNT0 = 0x64; //set count
 TCCR0 = 0x04; //start timer
}

#pragma interrupt_handler timer0_ovf_isr:10
void timer0_ovf_isr(void)
{
 TCNT0 = 0x64; //reload counter value
//  ad
    if(++time == 40){
        time = 0;
        ADCSR = 0xC6;               //  开始转换
        while(!(ADCSR & 0x10));     //  等待转换完成
        adc = ADCL;
        adc |= (int)(ADCH << 8);    //  注意顺序
        ADCSR = 0x10;               //  停止
        display[0] = adc%10;
        adc = adc / 10;
        display[1] = adc%10;
        adc = adc / 10;
        display[2] = adc%10;
        adc = adc / 10;
        display[3] = adc%10;
    }
//  end ad
//  display
    switch(dis){
        case  0:  write164(display[dis] | 0x70);  break;
        case  1:  write164(display[dis] | 0xB0);  break;
        case  2:  write164(display[dis] | 0xD0);  break;
        case  3:  write164(display[dis] | 0xE0);  break;
    }
    if(++dis > 3) dis = 0;
//end  display
}

//ADC initialisation
// Conversion time: 13uS
void adc_init(void)
{
 ADCSR = 0x00; //disable adc
 ADMUX = 0x00; //select adc input 0
 ACSR  = 0x80;
 ADCSR = 0x83;
}

//call this routine to initialise all peripherals
void init_devices(void)
{
 //stop errant interrupts until set up
 CLI(); //disable all interrupts
 DDRB = 0x01;    //  初始化操作74LS164的管脚
 DDRD = 0xC0;    //  初始化操作74LS164的管脚
 DDRC = 0x00;
 timer0_init();
 adc_init();

 MCUCR = 0x00;
 GICR  = 0x00;
 TIMSK = 0x01; //timer interrupt sources
 SEI(); //re-enable interrupts
 //all peripherals are now initialised
}

//
void main(void)
{
 init_devices();
 //insert your functional code here...
 while(1);
}