How Generate Signal with frequency and duty Cycle?(8051 Assembly)

[panda1234]

Hi,
suppose we have frequency and duty cycle in R7 and R6 now how generate signal with internal interrupt?
Thanks a lot

 

[KlausST]

Hi,

this is discussed very often.

It is also called "PWM generation" or "waveform generation".

check below the "similar threads"
and check other forum thread on this
and check wikipedia and google.

Good luck

Klaus

 

[panda1234]

Thanks but i want use internal interrupt only not instructions for PWM generating.

 

[KlausST]

Hi,

sure you can do this with interrupts.

The benifit of PWM generation is:
* low frequency jitter
* low duty cycle jitter
* extremely low and extremely high duty cycle possible
* no processing power needed (besides setup)

Klaus

 

[panda1234]

Thanks for your hints but first i want to generate it without PWM please help me for do that.

- - - Updated - - -

for example suppose i would like to have a signal 200 Hz and 45% duty cycle how to generate it with internal interrupt.

 

[KlausST]

Hi,

200 Hz is OK. it makes 5ms for a total cycle.

Now you have to decide what resolution you need.

Maybe 5%. This gives 20 steps. 20 steps in 5ms.
Means you need to generate interrupt with 200Hz x 20 = 4000Hz.

This means you need to setup your timer to generate an interrupt eveery 250us.

Within the ISR you need a counter.
increment the counter every time you enter the ISR. set it to zero if it is >=19.
So it counts 0 up to 19.
Now you have to compare this counter with your PWM value. ( in the range of 0...20)
if pwm_value > counter then set PWM_PORT, else clear PWM_PORT.
return from ISR
****

0 gives 0% duty cycle
1 give 5% duty cycle
...
19 gives 95% duty cycle
20 gives 100% duty cycle.

*****

Klaus