pwm_t2.c

用定时器实现的PWM程序,可设置占空比.

/*
 File:	pwm_t2.c
 说明:	PWM波形输出,定时器实现
 Author:wolfe
 Data:	2008.10 
*/


#include "at89x52.h"
#include "ES51_II.h"
#include "es51_ii_lib.h"

//	输出到P1.0,直接观察LED1亮度粗略地判断.
sbit PWM_OUT = P1^0;

//	全局变量
bit  bPWMFLAG;
unsigned int Revlue;		
unsigned int Positive;
unsigned int Negative;

//	timer2初始化程序
void InitTimer2(unsigned int value)
{
	RCAP2H = value>>8;
	RCAP2L = value;	
	T2MOD = 0x00;				//	禁止定时时钟从P1.0输出.
								//	计数方式与P1.1无关,采用加计数方式.
	TH2	= RCAP2H;	
	TL2	= RCAP2L;
	T2CON = 0x00;				//	0000,0000	计数,自动重装方式.
}

//	timer2中断程序
void T2OverflowINT(void) interrupt 5 using 0
{
	PWM_OUT = !PWM_OUT;
	TF2 = 0;					//清零中断标志	
	RCAP2H = Revlue>>8;			//重写RCAP寄存器
	RCAP2L = Revlue;
	
	if(0 == bPWMFLAG)			//设置下一次RCAP2H的值
		Revlue = Positive;
	else
		Revlue = Negative;	
	bPWMFLAG = !bPWMFLAG;
}


//	设置占空比(频率为1KHZ)
//		设置占空比范围:5.0%-95.0%;精确到小数后一位,
//		矩形波中占空比是指正脉冲与整个周期的比值.
void SetDutyCycle(float duty)
{
	bPWMFLAG = 0;
	PWM_OUT = 0;				//	PWM输出引脚初始状态为0
	Positive = 0xffff - 10*duty;
	Negative = 0xffff - 10*(100-duty);
	InitTimer2(Negative);
}

//	启动PWM输出
#define ENPWMOUT()	TR2=1	
//	停止PWM输出
#define DISPWMOUT()	TR2=0

void main()
{	
	EA = 1;						//	开总中断
	ET2 = 1;					//	允许T2溢出中断
								
								//	修改传递的参数,观察LED1灯的亮度.
	SetDutyCycle(53.4);			//	设置占空比为53.4%
							
	ENPWMOUT();					//	允许PWM输出
	while(1);
}