Yet another PWM question.

MichaelG · Guest

Hi

How can i get a 100hz PWM on a 16F877A @ 20mhz, in some of the topics there i some talk about software PWM but i dont really get (kind of a C newbie).

I would like to use that PWM to control the backlight/contrast on my GLCD but i dont know if its going to like a 1.2khz PWM??

Regards
MichaelG

Mark · Joined: 07 Sep 2003 Posts: 2838 Location: Atlanta, GA

You can't using the PWM module. You could use the Compare feature and toggle the pin in an interrupt. If the backlight is an LED, it won't care about the frequency being 1.2KHz.

MichaelG · Guest

The current LCD iam useing right now uses LEDs as backlight but in a few days ill be useing a Sharp LM32007T (320x200 pixel) display.

If iam going to use a hardware PWM at 1.2khz, how will i be able to use my 1ms interrupt routine?

Regards
MichaelG

Mark · Joined: 07 Sep 2003 Posts: 2838 Location: Atlanta, GA

Well if you are using Timer2 for the 1ms then you aren't going to get a 1.2KHz. You will have to settle for something a bit faster. The LED's won't care.

MichaelG · Guest

Ok, but assume that i will have a problem when switching to the Sharp LCD that is useing a CCFT backlight.

Regards
Michael.

Mark · Joined: 07 Sep 2003 Posts: 2838 Location: Atlanta, GA

You can't dim a CCFT by just supplying a pwm to the power. The driver for the CCFT would have to support the dimming.

MichaelG · Guest

Ok, tnx for your help.

Regards
Michael.