demo_11_2__.c

这是马潮老师最新力做<<AVR单片机潜入式系统原理与应用实践>>中有关实现频率计的C程序,用CVAVR编译,对想熟悉和学习AVR单片机的朋友一定有用.注释详细,一看就懂.

/*********************************************
File name			: demo_11_2.c
Chip type           : ATmega16
Program type        : Application
Clock frequency     : 4.000000 MHz
Memory model        : Small
External SRAM size  : 0
Data Stack size     : 256
*********************************************/

#include <mega16.h>
	#ifndef __SLEEP_DEFINED__
	#define __SLEEP_DEFINED__
	.EQU __se_bit=0x40
	.EQU __sm_mask=0xB0
	.EQU __sm_powerdown=0x20
	.EQU __sm_powersave=0x30
	.EQU __sm_standby=0xA0
	.EQU __sm_ext_standby=0xB0
	.EQU __sm_adc_noise_red=0x10
	.SET power_ctrl_reg=mcucr
	#endif
flash unsigned char led_7[10]={0x3F,0x06,0x5B,0x4F,0x66,0x6D,0x7D,0x07,0x7F,0x6F};
flash unsigned char position[8]={0x7f,0xbf,0xdf,0xef,0xf7,0xfb,0xfd,0xfe};

unsigned char dis_buff[8];				// 显示缓冲区，存放要显示的8个字符的段码值
unsigned char posit;
bit	freq_ok = 0;
unsigned char time2_new;
unsigned int freq;
unsigned long int freq_temp;

void display(void)				// 8位LED数码管动态扫描函数
{
	PORTC = 0xff;
	PORTA = led_7[dis_buff[posit]];
	if (posit==5) PORTA = PORTA | 0x80;
	PORTC = position[posit];
	if (++posit >=8 ) posit = 0;
}

// T/C0 比较匹配中断服务，250个计数脉冲中断一次
interrupt [TIM0_COMP] void timer0_comp_isr(void)
{
	time2_new = TCNT2;
	TCNT2 = 0;
	TIFR |= 0x02;
	freq_temp = freq;
	freq = 0;
	freq_ok = 1;
}

// T/C2 比较匹配中断服务，500us一次
interrupt [TIM2_COMP] void timer2_comp_isr(void)
{
	freq++;
	#asm("sei")		// 开中断，允许中断嵌套，T/C0中断可打断该中断服务
	display();
}

void freq_to_disbuff(void)		// 频率值转化为BCD码送显示缓冲区
{
	unsigned char i,j=7;
	for (i=0;i<=7;i++)
	{
		dis_buff[j-i] = freq_temp % 10;
		freq_temp = freq_temp / 10;
	}
}

void main(void)
{
    unsigned char i;
    DDRA=0xFF;			// LED数码管
    DDRC=0xFF;
    // T/C2初始化
    TCCR2=0x0A;			// 内部时钟，8分频（4M/8=500KHz），CTC模式，
    TCNT2=0x00;			// 基时为2us
    OCR2=0xF9;			// OCR2 = 0xF9(249),(249+1)/500 = 0.5ms
	// T/C0初始化
    TCCR0=0x0E;			// 外部T0脚下降沿触发计数，CTC模式
    TCNT0=0x00;
    OCR0=0xF9;			// OCR0 = 0xF9(249),(249 + 1) = 250

    TIMSK=0x82;			// 允许T/C2、T/C0比较匹配中断

    for (i=0;i<=7;i++)dis_buff[i]=0;

    #asm("sei")			// 开放全局中断

    while (1)
    {
		if (freq_ok)
		{
			freq_temp = freq_temp * 250 + time2_new;	// 累计250个脉冲的时间间隔
			freq_temp = 12500000000/freq_temp;		// 换算成频率
			freq_to_disbuff();						// 频率值送显示
			freq_ok = 0;
		}
    }
}