PWM frequency

how change frequency period on 5ms? need control servos without worrying functions may take on 20ms execute.

i'm pouring on register descriptions in atmega168 datasheet , it's not clear have change.

i can't lower clock rate. external servo controller option don't idea.

edit:
i found this:
http://www.arduino.cc/cgi-bin/yabb2/yabb.pl?num=1170282999

quote

thanks hints, mellis.

after hours of diggin' in datasheets , webpages came solution works:
(hope it's of interest)

quote

/* servopwm
* ---------------
*
* comments
*
* (copyright notice) 2007 moe
* <http://youraddress.here>
* <mailto:you@youraddress.here>
*
*/

int val = 0;

void setup(void) {
 pinmode(9,output);  // servo pin
 serial.begin(9600);

 tccr1a = 0x00;      // sets timer control bits pwm phase , frequency correct mode
 tccr1b = 0x12;      // sets timer control bits prescaler n = 8
 icr1 = 0x0fa0;      // upper timer limit = 4000 (in hex) equals 4ms => 1/5 of servo frequency

}

void loop(void) {
 val = analogread(0);      // read potentiometer
 val = (val * 1.76) + 600; // convert potentiometer reading value in microseconds (my servo responds signals in 600us - 2400us range)
 analogwrite(9,val);       // pulse servo
 serial.println(val);      // output servo value

}

what does:

- initializes pwm timer frequency 4ms - 1/5 of servo's frequency of 20ms
 (as of servo's signals fall in between 0.5ms - 2.5ms range).
- analogwrite takes values 0 4000 (for = 0.001ms)

edit:

it works on pins 9 , 10 timer1 drives these two.

best regards,
moe

what timer0 , timer2? know 8 bits, do this?

tccr0a = 0x00;
tccr0b = 0x12;
tccr2a = 0x00;
tccr2b = 0x12;

thanks

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