Hello All,

    I've made some alterations and put a lot of comments (in english this
time :) in my frequency counting routine (code is on the end of this email),
but it's still not working very well.

    When I put a square-wave of 1,000 Hz, it counts 2480 instructions for a
complete cycle when the correct would be 2500. Also, it tells readings like:
        2480, 2480, 2425, 2480, 2425

    I think this is really strange. The reading are more weird with lower or
higher frequencies.

    Can someone take a look at my routine? I think it deserves a good look,
because It works on a different way from the common
count-cycles-for-a-second approach.

    Best regards,

    Brusque

-----------------------------------
Edson Brusque
Research and Development
C.I.Tronics Lighting Designers Ltda
(47) 323-2685  /  (47) 9993-6453
Blumenau  -  SC  -  Brazil
www.citronics.com.br
-----------------------------------

****************************************
* PIC Frequency Counting using CCS PIC-C
****************************************

uns16 interrupt_counter;

// This interrupt is used during the frequency counting routine to
// implement a 32 bit counter
#INT_GLOBAL
void interrupt(void)
{
 interrupt_counter++;
 PIR1.TMR1IF = 0;
}

// This routine counts the frequency by getting the time (in instructions)
// it takes to complete 32 cycles
uns16 get_freq(void)
{
 uns8 x;
 uns8 counter;
 float total;

 // Now we're setting the Timer1 interrupt
 PIR1.TMR1IF = 0;
 PIE1.TMR1IE = 1;
 INTCON.PEIE = 1;
 INTCON.GIE  = 1;

 // Now we're setting the Timer1 itself
 T1CON.T1CKPS1 = 0;
 T1CON.T1CKPS0 = 0;
// T1CON.T1OSCEN = 1;
 T1CON.NOT_T1SYNC = 1;
 T1CON.TMR1CS  = 0;
 T1CON.TMR1ON  = 0;

 // Clearing the counter (we're, obviously, using the TMR1 for this)
 interrupt_counter = 0;
 TMR1H = 0;
 TMR1L = 0;

 // Setting the direction for the pin we'll use to detect the cycles
 TRISC.B7 = 1;

 // Waiting for the end of the actual cycle
 while(!PORTC.B7);
 while(PORTC.B7);

 // Counting the time (in instructions) that it takes to detect 32 cycles
 T1CON.TMR1ON = 1;
 for (x=0; x < 32; x++) {
  while(!PORTC.B7);
  while(PORTC.B7);
 }
 T1CON.TMR1ON = 0;

 // Calculating the frequency from the time in instructions
 total = ((float)interrupt_counter * 65536) + ((float)TMR1H * 256) +
((float)TMR1L);
 total /= 32;
 total = 2500000 / total;
 // 2500000 is for a 10MHz clock (2,500,000 instructions for sec)

 return total;
}

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