demo_11_2.i

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

// CodeVisionAVR C Compiler
// (C) 1998-2001 Pavel Haiduc, HP InfoTech S.R.L.

// I/O registers definitions for the ATmega16


#pragma used+
sfrb TWBR=0;
sfrb TWSR=1;
sfrb TWAR=2;
sfrb TWDR=3;
sfrb ADCL=4;
sfrb ADCH=5;
sfrw ADCW=4;      // 16 bit access
sfrb ADCSRA=6;
sfrb ADMUX=7;
sfrb ACSR=8;
sfrb UBRRL=9;
sfrb UCSRB=0xa;
sfrb UCSRA=0xb;
sfrb UDR=0xc;
sfrb SPCR=0xd;
sfrb SPSR=0xe;
sfrb SPDR=0xf;
sfrb PIND=0x10;
sfrb DDRD=0x11;
sfrb PORTD=0x12;
sfrb PINC=0x13;
sfrb DDRC=0x14;
sfrb PORTC=0x15;
sfrb PINB=0x16;
sfrb DDRB=0x17;
sfrb PORTB=0x18;
sfrb PINA=0x19;
sfrb DDRA=0x1a;
sfrb PORTA=0x1b;
sfrb EECR=0x1c;
sfrb EEDR=0x1d;
sfrb EEARL=0x1e;
sfrb EEARH=0x1f;
sfrw EEAR=0x1e;   // 16 bit access
sfrb UBRRH=0x20;
sfrb UCSRC=0X20;
sfrb WDTCR=0x21;
sfrb ASSR=0x22;
sfrb OCR2=0x23;
sfrb TCNT2=0x24;
sfrb TCCR2=0x25;
sfrb ICR1L=0x26;
sfrb ICR1H=0x27;
sfrb OCR1BL=0x28;
sfrb OCR1BH=0x29;
sfrw OCR1B=0x28;  // 16 bit access
sfrb OCR1AL=0x2a;
sfrb OCR1AH=0x2b;
sfrw OCR1A=0x2a;  // 16 bit access
sfrb TCNT1L=0x2c;
sfrb TCNT1H=0x2d;
sfrw TCNT1=0x2c;  // 16 bit access
sfrb TCCR1B=0x2e;
sfrb TCCR1A=0x2f;
sfrb SFIOR=0x30;
sfrb OSCCAL=0x31;
sfrb OCDR=0x31;
sfrb TCNT0=0x32;
sfrb TCCR0=0x33;
sfrb MCUCSR=0x34;
sfrb MCUCR=0x35;
sfrb TWCR=0x36;
sfrb SPMCR=0x37;
sfrb TIFR=0x38;
sfrb TIMSK=0x39;
sfrb GIFR=0x3a;
sfrb GICR=0x3b;
sfrb OCR0=0X3c;
sfrb SPL=0x3d;
sfrb SPH=0x3e;
sfrb SREG=0x3f;
#pragma used-

// Interrupt vectors definitions


// Needed by the power management functions (sleep.h)
#asm
	#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
#endasm


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 [20] 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 [4] 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;
		}
    }
}