I want to generate a software PWM signal for 5 millisecond. using GPIO with 50 percent duty cycle and 100 KHz.
While(5ms)
{
PIN = 1;
delay_micro(10);
PIN = 0;
delay_micro(5);
PIN = 1;
}
Is this correct or I want to do any thing else.
Electronic – Generate PWM signal using GPIO
pwm
Related Solutions
You can do this in software and keep track of all the required timing yourself, but most microcontrollers have hardware that can generate PWM autonomous after you initialize it. The basic things are a timer/counter and an Output Compare Register (OCR):
The counter continuously increments, represented by the slope, and is compared with the OCR. The PWM output goes low when the counter exceeds the OCR, and goes high again when it resets. The 5 % resolution you need (20 steps) is not a problem; a 16 bit timer can generate PWM with a better than 0.002 % resolution, and even an 8 bit timer can do 0.4 %.
All you have to do is program a new value in the OCR. The lower the value, the smaller the pulse width. The following animation is from this site:
Further reading
Using the AVR’s High-speed PWM, an Atmel application note.
ATMega32 datasheet describes on page 69 ff. how to use Timer0 for PWM operation.
On the bottom of page 350 of the microcontroller datasheet, it mentions that writing a small value to the timer value register during the overflow interrupt might cause the next interrupt to be triggered only on the next pwm iteration, since the timer continues to count while the interrupt routine is being executed.
An unsynchronized write to the TIM channel registers to change a pulse width value could cause incorrect operation for up to two PWM periods. For example, writing a new value before the counter reaches the old value but after the counter reaches the new value prevents any compare during that PWM period. Also, using a TIM overflow interrupt routine to write a new, smaller pulse width value may cause the compare to be missed. The TIM may pass the new value before it is written.
This is confirmed by the fact that the pwm value is held high for one entire pwm clock period + what looks like the timer length (based on the surrounding lengths). The value being written to the timer length register is probably close to 0 at the time of error, so it is quite viable that the counter has passed the smaller value during the interrupt, and would only trigger on the following cycle.
This could be fixed by increasing the sinusoid minimum level to a level higher than the time it takes to execute the ISR, or changing the mechanism by which the new level is set. The top of page 351 details how this may be done.
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Best Answer
I'm not a big fan of the "delay" functions because they delay your whole program. I have also made this recently and to get a proper PWM I used the timer0 interrupt to toggle the outputpin every time an interrupt occurs. You can also work with a counting-loop so by example the interrupt has to occur 10 times before the output toggles.
Here is an example which worked fine for me with a PWM frequency of 1kHz. (timer0 is 8-bit timer)
void interrupt interrupts(void) { if (INTCONbits.TMR0IF == 1) { //interrupt from timer0 TMR0 = 0x06; //reload timer0 PIN1 = !PIN1; if (timer0_tick_count >= speed) { //count-loop with variable speed timer0_tick_count = 0;} else { timer0_tick_count++; } INTCONbits.TMR0IF = 0; }}