PWM - Duty cycle - Is finer adjustment possible?

[atferrari]

Today I started to experiment with PWM in a 16F877. Got both PWM modules working in minutes.

While period can be finely ajusted with 10-bits precision, the duty cycle seems more complicate due to the two LSB in CCP1CON<5:4>.

I have no specific application in mind but when tried to increase/decrease the duty cycle value I've realized that trying to change it down to the LSB would demand too much code other than INCF / DECF.

For an eventual application requiring a fast adjustment, is it any way to do it or we have to accept adjusting only the value in CCPR1L?

Agustín Tomás

 

[maui]

atferrari,


What do you mean too much code ?

If you mean that the code takes too long to modify the PWM and makes cracks and pops you can make a shadow register in software. copy the PWM controll register into a general purpose register modify what you want in it, then copy that back.to the PWM controll register.

Maui

 

[atferrari]

Hi Maui,

I asume that you know the 16F877. To control duty cycle, there is one 8-bit register plus 2 more (the LSB) which go in another register. Together they make for a 10 bit value.

My counter should then be 16-bit from from where I should take the two LSB to insert in the CCP1CON <5:4> and the 8 left into CCPR1L.

However it's done, it always seems too much code. Thinking of something simpler I didn't even tried to write that.

Agustín Tomás