need one pin with 22kHz , it's possible ??

[jruibarroso]

i'm using an 16F870 and when i need i'll like to generate 22kHz on a pin, can any help me ?

[Ttelmah]

It depends what clock rate you are running the chip at.
The CCP module, is designed to do exactly this, but the actual possible frequencies depend on the source. So if (for instance), you are running off 8MHz, you can generate a clock at 22222Hz or 21978Hz. However if you choose a crystal that is a nice multiple of 22000 (such as 8.8MHz), you can get the frequency exactly.

Best Wishes

[jruibarroso]

Yes, i know that .. but my problem is not the acuracy of the output but how can i generate this in C , if anybody could write some lines of code for i understand how to do it . THANK you ALL

[Ttelmah]

To actually 'give you the lines', we need to know the frequency.
However:

setup_ccp1(CCP_PWM);

sets the CCP, to run in PWM mode.

Then the frequency is set with:

setup_timer_2(T2_DIV_BY_1,90,1);

Which will set T2, to run from the master clock/4, and count from 0 to 90 (91 counts). With an 8MHz source,this will give 21978Hz.
Then to give a 50:50 mark space ratio, you would need:

set_pwm1_duty(182L);

Note the 'L'. The duty cycle, can count from the timer master clock, or from the actual source clock (at four times this frequency). If you give the 'duty' command, a _short_ integer, it is set in counts of the timer clock, and only has 1/4 the resolution. If you give it a 'long' integer, it is set in counts of the undivided master clock, so the possible counts are then 91*4.

I'd suggest you consider phrasing questions a bit more carefully. If you 'know' that the PWM/CCP, can give you the required frequency, then a question like:

"How do I set up the PWM, on a PIC 16F870, using C", is much more likely to get the answer. By asking for a specific frequency, and then not giving the data needed f the calculations (what frequency you are running off), you are not helping yourself get an answer quickly.

Look at ex_pwm, for an example of setting different frequencies.

Best Wishes

[jruibarroso]

thank you , and sorry for my phrase .

One more question .. with this code , where do i define a output pin for output this 22khz signal ?

[Ttelmah]

You don't. It is fixed in the hardware. On the 16F870, the CCP1 pin, is port C, pin 2. Look at the chip's data sheet. On some of the latter chips, the pin can be changed (this is normally a 'fuse' setting), but on the 870, there is only one pin supporting this feature.

Best Wishes