external oscillation

[lerameur]

Hello,

I would like to know if it possible to create 20KhZ external frequency with Pic chips, lets say the pic16f88. I did not find anything on google on such a thing.

thank you

ken

[sayzer]

If what you want is to generate 20Khz frequency using 16F88, then sure you can do it by using PWM feature of this PIC.

For 20Khz at 4Mhz, using 1:1 prescaler, PR2 should be 49.
At 20Mhz, 1:1, PR=249.



mister_e, pls correct me if I am wrong

[mister_e]

Yup PWM is the way to go. You can use the PBP HPWM or setting the PIC register as Sayzer said.

mister_e, pls correct me if I am wrong

I got the same results

[lerameur]

I got it going with a 4Mhz oscillator. Here is the program.
I wanetd to use the 20Mhz oscillator. and it do not work. I change the 4 to a 20 in the program and changes the crystal and the capacitor to 22pF and it is not oscillating, anybody knows why. is there a command I nee to do ?


Define LOADER_USED 1
DEFINE OSC 4 'Using 4MHz oscillator
TRISB = 0

loop: FREQOUT PORTB.1,10000,20000 ' Turn on PORTB for 1- sec at20Khz
Pause 100 ' Delay for .5 seconds

Goto loop ' Go back to loop and blink LED forever

[lerameur]

ok added this line :

@ DEVICE HS_OSC

and now it works

[lerameur]

I am trying ot get a sin wave at the output. From the manuals of picbasic pro, they say to add a low pass filter, I did this, it dos remove the extra noise, but it does not make it a sinwave. Anybody know how to make it a sin wave ?

ken