Calculate frequency

[Jaco Malan]

Hi There
I am very new to electronics/pics and desperately need help in calculating frequency, I often need(plan) to use different frequencies for my projects but really struggle with the calculation.
I use a 16F630 in a small frequency generator.

case 1: // 136.1Hz
timer1_reload = 0xb856;
timer1_highcount = 0;
break;

Is there an easy way to calculate the frequency?

Thanks for any help you guys can offer

Jaco

 

[Wp100]

Hi,

You can download this free utility if it looks like what you need.

 

[MikeMl]

Go to Roman Black's web site and read. (Mr RB)

 

[Mr RB]

Thanks Mike, I guess you are talking about this code;

/******************************************************************************
  ZeroJitter.c   Generates zero-error and zero jitter interrupt period.
  Open-source  -  21 Nov 2009  -  www.RomanBlack.com/one_sec.htm

  PIC 12F675, 4MHz xtal.
  This is like my zero-error 1 second timing system, that uses a convenient
  constant to set ANY period (with 1 timer tick resolution).
  However this system has zero jitter!
  Can be used to generate 1 second period, or 50Hz freq output etc.
******************************************************************************/

// PERIOD sets the pin toggle freq; toggle PERIOD = (xtal / 4 / freq / 2) 
#define PERIOD 10000   // (xtal 4Mhz) TMR0 1MHz, 10000 = 100Hz toggle (50Hz output)

#define PER_COUNTS ((PERIOD / 100) - 1)  // don't edit this!
#define PER_REMAINDER (PERIOD - (PER_COUNTS * 100))  // don't edit this!

unsigned int pcount;    // used in interrupt to count PER_COUNTS 
//-----------------------------------------------------------------------------


//+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
void interrupt()
{
  //-----------------------------------------------------
  // this is the TMR0 overflow interrupt.
  // Note! TMR0 has a 3 tick write latency, writes must be -3
  //-----------------------------------------------------
  // check if time to toggle the output pin
  if(!pcount)
  {
    asm {
      movlw 0x01      ; // mask for pin 0
      xorwf GPIO,f    ; // toggle PIC pin GPIO.0
    }
    pcount = (PER_COUNTS+1);    // how many delays to make total
    TMR0 -= (PER_REMAINDER-3);  // first delay will be ==remainder
  }
  // else make a normal delay
  else
  {
    TMR0 -= (100-3);       // make another 100 tick delay
  }
  pcount--;
  //-----------------------------------------------------
  // clear the TMR0 overflow flag and exit
  INTCON.T0IF = 0;
}
//+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++


//=============================================================================
//   MAIN
//=============================================================================
void main ()
{
  //-----------------------------------------------------
  // PIC 12F675  setup ports
  ANSEL = 0;            // ADC off
  CMCON = 0x07;         // comparators off
  GPIO =   0b00000000;  // clear GPIO
  TRISIO = 0b00000000;  // All outputs
  WPU =    0b00000000;  // pin pullups; 1 = pullup on (for button)

  //-----------------------------------------------------
  // timer setup etc
  OPTION_REG = 0b00001000;    // TMR0 on, 1:1 prescale
  pcount = 0;
  INTCON = 0b10100000;  // GIE on, T0IE on (turn interrupt on) 

  //-----------------------------------------------------
  // main run loop here
  while(1)
  {
    continue;   // loop and do nothing, just let the interrupt happen
  }
}
//-----------------------------------------------------------------------------

Jaco- You only need to change that PERIOD value in the top of the code and it will generate the frequency for you.

toggle PERIOD = (xtal / 4 / freq / 2)

so for 4MHz xtal and 136.1Hz;

PERIOD = 4000000 / 4 / 136.1 / 2
PERIOD = 3674