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This code implements pulse width modulation (PWM) on an 8051 microcontroller to control the duty cycle of a signal. It initializes ports and a timer, sets the PWM frequency, and uses an interrupt service routine to toggle a pin on and off to generate the PWM signal. The duty cycle is controlled by varying a value between 0-255. A timer overflow interrupt occurs every PWM cycle to accurately toggle the pin.

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jitendra jha
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56 views2 pages

Code Text

This code implements pulse width modulation (PWM) on an 8051 microcontroller to control the duty cycle of a signal. It initializes ports and a timer, sets the PWM frequency, and uses an interrupt service routine to toggle a pin on and off to generate the PWM signal. The duty cycle is controlled by varying a value between 0-255. A timer overflow interrupt occurs every PWM cycle to accurately toggle the pin.

Uploaded by

jitendra jha
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
Available Formats
Download as TXT, PDF, TXT or read online on Scribd
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#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 257 // Highest possible PWM Frequency

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

PWM = 28; // 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
}

[http://www.8051projects.net/wiki/Pulse_Width_Modulation] -asm code

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