Help to generated square wave!

[blinkstar88]

Hi i'm new on CCS, i need to generated multiple square wave (38Khz,76KHz, 304Khz,19Khz) on portB using 4.864Mhz crystal. I get the following code from Example of CCS:
But i don't know to change the code for this freq. Please help.
Any idea and help very aprreciated
Thanks

#if defined(__PCM__)
#include <16F628a.h>
#fuses HS,NOWDT,NOPROTECT,NOLVP
#use delay(clock=4864000)

#elif defined(__PCH__)
#include <18F452.h>
#fuses HS,NOWDT,NOPROTECT,NOLVP
#use delay(clock=4864000)
#endif

#define NUM_OUTPUTS 8

//NOTE: periods MUST be multiples of 400
//Periods are in microseconds
#define PERIOD_0 400
#define PERIOD_1 800
#define PERIOD_2 1600
#define PERIOD_3 2000
#define PERIOD_4 20000
#define PERIOD_5 64000
#define PERIOD_6 2000000
#define PERIOD_7 2800000

const long wave_period[NUM_OUTPUTS] = {
PERIOD_0/400, PERIOD_1/400, PERIOD_2/400, PERIOD_3/400,
PERIOD_4/400, PERIOD_5/400, PERIOD_6/400,PERIOD_7/400};

long counter[NUM_OUTPUTS] = {0,0,0,0,0,0,0,0};

int port_b_image;


// This interrupt is used to output the waveforms. The interrupt
// is automatically called ever 200us.
#INT_TIMER1
void wave_timer() {
int i;

set_timer1(0xFC4F); // sets timer to interrupt in 200us
output_b(port_b_image); // outputs the waveform

for(i=0; i<NUM_OUTPUTS; i++) // sets up next output for each pin
{
if((++counter[i]) == wave_period[i]) // if counter is expired
{
counter[i] = 0; // reset counter
if(bit_test(port_b_image,i)) // and set pin as needed
bit_clear(port_b_image,i);
else
bit_set(port_b_image,i);
}
}
}


void main() {

setup_timer_1(T1_INTERNAL|T1_DIV_BY_1); // setup interrupts
enable_interrupts(INT_TIMER1);
enable_interrupts(GLOBAL);

port_b_image=0; // initialize variable
output_b(port_b_image);

while(TRUE); // loop forever
}

===================================================

[SherpaDoug]

That code only generates up to 25kHz square waves. You might be able to squeeze out 38kHz, but I don't think 76kHz and 304kHz with only a 4.86MHz crystal can be done. You can get some more speed with a faster crystal but 304kHz is going to be hard. You will have to poll timers rather than using interrupts.

Years ago I did a synthesizer (numerically controlled oscillator) that did 32kHz or maybe 35kHz on a PIC16C54 running at 20MHz but it was tough.

If you can make do with even power of 2 divisions of the clock frequency (303.75kHz etc.) it will be easier. Read the PIC datasheet section about timers to get a feel for what can be done.
_________________
The search for better is endless. Instead simply find very good and get the job done.

[blinkstar88]

SherpaDoug, Thank for the replay.

I want to use this code for FM Encoder stereo from Broadcast Warehouse, they design using crystal 4.864Mhz and Pic16c620. They generated 8 freq in realtime (PortB pin0 = 38Khz, Portb Pin 1 = 114 Khz, Portb Pin 2 = 114Khz, Portb Pin 3 = 38Khz) and at PORTB 4 - 7 = 19KHZ,57KHZ,133KHZ and 95Khz, the sum for each side (PORTB0-3 and other side (portb4 -7) is 304Khz.

Do you have any idea what code will i using to make it work.
It's possible to using PWM for multiple PORTB?

Thanks

[SherpaDoug]

It sounds like you are going to have to get real familiar with the hardware of your PIC. The data sheet is only 128 pages as that chip is fairly simple. I suggest you read all about how its clocks and timers work, an afternoon's reading. It will be a good investment for any PIC work in the future.

(Print relevant sections to paper or you will go mad trying to make sense of it on a PC screen.)
_________________
The search for better is endless. Instead simply find very good and get the job done.

[blinkstar88]

Thanks,
I was read all the datasheet, but i'm still not get the light :( .May be a little code give me away where to start.