PWM 8051

Chào các bạn trong bài đăng này mình sẽ giới thiệu với các bạn về PWM 8051.

Ảnh mô phỏng proteus.

#include<reg51.h>

// PWM_Pin
sbit PWM_Pin = P2^0;   // Pin P2.0 is named as PWM_Pin

// Function declarations
void cct_init(void);
void InitTimer0(void);
void InitPWM(void);

// Global variables
unsigned char PWM = 0;  // It can have a value from 0 (0% duty cycle) to 255 (100% duty cycle)
unsigned int temp = 0;    // Used inside Timer0 ISR

// PWM frequency selector
/* PWM_Freq_Num can have values in between 1 to 257 only
 * When PWM_Freq_Num is equal to 1, then it means highest PWM frequency
 * which is approximately 1000000/(1*255) = 3.9kHz
 * When PWM_Freq_Num is equal to 257, then it means lowest PWM frequency
 * which is approximately 1000000/(257*255) = 15Hz
 *
 * So, in general you can calculate PWM frequency by using the formula
 *     PWM Frequency = 1000000/(PWM_Freq_Num*255)
 */
#define PWM_Freq_Num   1 // Highest possible PWM Frequency


// Main Function
int main(void)
{
   cct_init();         // Make all ports zero
   InitPWM();              // Start PWM

   PWM = 127;              // Make 50% duty cycle of PWM

   while(1)                // Rest is done in Timer0 interrupt
   {}
}

// Init CCT function
void cct_init(void)
{
P0 = 0x00;   
P1 = 0x00;   
P2 = 0x00;   
P3 = 0x00;  
}

// Timer0 initialize
void InitTimer0(void)
{
TMOD &= 0xF0;    // Clear 4bit field for timer0
TMOD |= 0x01;    // Set timer0 in mode 1 = 16bit mode

TH0 = 0x00;      // First time value
TL0 = 0x00;      // Set arbitrarily zero

ET0 = 1;         // Enable Timer0 interrupts
EA  = 1;         // Global interrupt enable

TR0 = 1;         // Start Timer 0
}

// PWM initialize
void InitPWM(void)
{
PWM = 0;         // Initialize with 0% duty cycle
InitTimer0();    // Initialize timer0 to start generating interrupts
// PWM generation code is written inside the Timer0 ISR
}

// Timer0 ISR
void Timer0_ISR (void) interrupt 1   
{
TR0 = 0;    // Stop Timer 0

if(PWM_Pin) // if PWM_Pin is high
{
PWM_Pin = 0;
temp = (255-PWM)*PWM_Freq_Num;
TH0  = 0xFF - (temp>>8)&0xFF;
TL0  = 0xFF - temp&0xFF;
}
else     // if PWM_Pin is low
{
PWM_Pin = 1;
temp = PWM*PWM_Freq_Num;
TH0  = 0xFF - (temp>>8)&0xFF;
TL0  = 0xFF - temp&0xFF;
}

TF0 = 0;     // Clear the interrupt flag
TR0 = 1;     // Start Timer 0
}

Link download project.
http://zo.ee/1WaL

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