PIC 12F629 as Frequency Divider

[deesarus]

Hello all,
I am a newbie to PIC-C programming,and am trying to develop a PIC-C program for frequency division.I have to use a PIC 12F629,that has to divide the input frequency by 32.I am using an external RC circuitry,that will change to give different values of input frequency.Thus,for example,if the input freq is 3.2 MHz,which will be supplied at Pin2..which is the GP5 pin...I shld produce a Sqaure wave of 100 KHz at Pin5..which is GP2.
I wud really appreciate any pointers and suggestions.I tried to see if I could use the CCP module,but it turns out the 12f629 does not have it.I find the Timer registers function confusing.I wrote a program to calculate the frequency at Pin 2,then divide that by 8,and output a sqaure wave at pin 5,based on that program.but it doesnt seem to be rite.
Any suggestions are gladly appreciated.
Thanks.

[Mark]

[Libor]

You can use the 12F629 PIC's TIMER0 module as a counter with GP2/T0CKI pin as a clock source, then all you have to do is set the output pin to the counter value's corresponding bit to achieve a division by 32.

I have not tried it, use this code fragment as a clue only, I may have made errors:

#include <12F629.h>
#fuses NOCPD,PROTECT,MCLR,PUT,INTRC_IO,BROWNOUT
#use delay(clock=4000000)
#use fast_io(A)

void main() {
int i;
set_tris_a(0b11011111); //GP5 output, all others input
setup_comparator(NC_NC); //no comparator, make all ports digital I/O
setup_timer_0(RTCC_EXT_L_TO_H | RTCC_DIV_1) //count low to high transitions on GP2

while (TRUE) { //do it forever
i = get_timer0(); //get counter value into i
output_bit(PIN_A5, bit_test(i, 5)); //output counter's 5th bit
}
}

[languer]

Edit:
I believe this may be off by, oh... say 255*2 counts. After getting my beauty rest, I realized that you are getting counts every 100kHz (using the 3.2MHz clock) on the timer so you only need one count.

So you need to divide-by-16 (not 32), and set timer0 to 255, this way everytime it counts once it rolls over and sets the interrupt. The div-by-16 is there so you toggle at twice the desired frequency, giving you in effect the desired clock output.

You can also not divide down, and count 16 to interrupt (set timer0 to 256-16). This would give you a programmable divider with a maximum of 255). Unfortunately, you have to limit the maximum output frequency well below the master clock so you can do the output toggling. You may need to use a higher master clock (e.g. 16-20MHz) to give you room to do the interrupt service and bit toggling. As it is you only have 4 instruction cycles (with 4MHz master clock), and 200kHz toggling rate.

Clear as mud...

I have not tried this but have done something similar. This should get you started. For the frequencies you're referring to (i.e. 3.2MHz), counting with the internal clock (4MHz / 4 =1MHz) will not get you there. For this you have to use the timer function.

Example Code: