51 Study Notes: Using Timer 0 to generate a PWM wave with a maximum period of 16s (STC12C5A60S2)

Hardware: STC12C5A60S2

Function: To realize PWM wave generation. The program cycle is 256ms and the output port is P1.3.

Code:

#include "reg51.h"

#include "intrins.h"

#define DARK 11059260L

#define T1MS (65536-FOSC/12/1000)

//The pulse generated by the timer is about 1MS, and the time after PWM is divided by 256 is 256ms

//By adjusting the value of T1MS, the maximum cycle time of PWM is 16s.

typedef unsigned char BYTE;

typedef unsigned int WORD;

/*Declare SFR associated with the PCA */

sfr CCON = 0xD8; //PCA control register

sbit CCF0 = CCON^0; //PCA module-0 interrupt flag

sbit CCF1 = CCON^1; //PCA module-1 interrupt flag

sbit CR = CCON^6; //PCA timer run control bit

sbit CF = CCON^7; //PCA timer overflow flag

sfr CMOD = 0xD9; //PCA mode register

sfr CL = 0xE9; //PCA base timer LOW

sfr CH = 0xF9; //PCA base timer HIGH

sfr CCAPM0 = 0xDA; //PCA module-0 mode register

sfr CCAP0L = 0xEA; //PCA module-0 capture register LOW

sfr CCAP0H = 0xFA; //PCA module-0 capture register HIGH

sfr CCAPM1 = 0xDB; //PCA module-1 mode register

sfr CCAP1L = 0xEB; //PCA module-1 capture register LOW

sfr CCAP1H = 0xFB; //PCA module-1 capture register HIGH

sfr PCAPWM0 = 0xf2;

sfr PCAPWM1 = 0xf3;

void Delay_xms(unsigned int z){

unsigned char i, j;

unsigned int k;

for(k=0;k

_nop_();

_nop_();

i = 12;

j = 84;

do{while (--j);}

while (--i);

}

}

// Initialize timer 0

void Time0Init()

{

TMOD = 0x01;

TL0=T1MS;

TH0=T1MS>>8;

TR0=1;

ET0=1;

EA=1;

}

void PWMInit()

{

CCON = 0; //Initial PCA control register

//PCA timer stop running

//Clear CF flag

//Clear all module interrupt flag

CL = 0; //Reset PCA base timer

CH = 0;

//    CMOD = 0x00; //Set PCA timer clock source as Fosc/2

CMOD = 0x04;

//Disable PCA timer overflow interrupt

CCAP0H = CCAP0L = 0x80; //PWM0 port output 50% duty cycle square wave

CCAPM0 = 0x42; //The device is timer 0 overflow pulse

CCAP1H = CCAP1L = 0xff; //PWM1 port output 0% duty cycle square wave

PCAPWM1 = 0x03;

CCAPM1 = 0x42; //PCA module-1 work in 8-bit PWM mode

//and no PCA interrupt

CR = 1; //PCA timer start run

}

void PWMSet(float a) //Input a represents the duty cycle

{

CCAP0H =CCAP0L =(BYTE)((1-a)*256);

}

void main()

{

Time0Init();

PWMInit();

PWMSet(0.1);

while(1)

{

PWMSet(0.5); //duty cycle is 50%

Delay_xms(2000);

}

}

//Timer 0 interrupt

void tm0_isr() interrupt 1 using 1

{

TL0=T1MS;

TH0=T1MS>>8;

}