To generate a PWM sine wave using a PIC16F877A microcontroller, you can use the following steps:
1)Configure the Timer2 module of the PIC16F877A microcontroller to generate a PWM signal. The PWM frequency can be set by configuring the PR2
register and the duty cycle can be set by configuring the CCPR1L and CCP1CON registers.
2)Generate a sine wave lookup table using a spreadsheet software or an online tool. The lookup table should contain the sine values for one cycle of the wave, ranging from 0 to 2π.
3)Store the sine wave lookup table in the program memory of the microcontroller.
4) Set up a Timer1 module of the PIC16F877A microcontroller to generate interrupts at a frequency that is equal to the desired frequency of the sine wave. In the interrupt service routine (ISR) for Timer1, read the values from the sine wave lookup table and update the duty cycle of the PWM
signal generated by Timer2.
#include
// sine wave lookup table
const unsigned char sine_table[64] = {128,140,152,163,174,185,195,205,214,222,230,237,243,248,252,255,
255,255,252,248,243,237,230,222,214,205,195,185,174,163,152,140,
128,116,104,93,82,71,61,51,42,34,26,19,13,8,4,0,
0,0,4,8,13,19,26,34,42,51,61,71,82,93,104,116};
// timer1 ISR
void __interrupt() timer1_isr(void) {
static unsigned char table_index = 0;
// update duty cycle of PWM signal generated by timer2
CCPR1L = sine_table[table_index];
// increment table index
table_index++;
if (table_index >= 64) {
table_index = 0;
}
}
void main(void) {
// configure timer2 for PWM generation
T2CON = 0b00000111; // prescaler = 1, postscaler = 1, timer2 on
PR2 = 255; // set PWM frequency
CCP1CON = 0b00001100; // PWM mode, PWM duty cycle controlled by CCPR1L
// configure timer1 for interrupt generation
T1CON = 0b00110101; // prescaler = 8, timer1 on, enable timer1 interrupt
TMR1IF = 0; // clear timer1 interrupt flag
TMR1H = 0xFC; // set timer1 reload value for 50 Hz interrupt frequency
TMR1L = 0x18;
PEIE = 1; // enable peripheral interrupts
GIE = 1; // enable global interrupts
while (1) {
// main program loop
}
}
In this example code, the sine wave lookup table contains 64 values, so the Timer1 module is configured to generate interrupts at a frequency of 50 Hz (the table is updated once per cycle). The Timer2 module is configured to generate a PWM signal with a frequency of 8 kHz. The duty cycle of the PWM signal is updated in the Timer1 ISR by reading the values from the sine wave lookup table.
