Hello,

    I've made a routine to make frequency counting with CCS. Code snipet
follow:

uns16 interrupt_counter;

#INT_TIMER1
void interrupt(void)
{
 interrupt_counter++;
}

uns16 get_freq(void)
{
 uns8 x;
 uns8 counter;
 float total;

 PIR1.TMR1IF =3D 0;
 PIE1.TMR1IE =3D 1;
 INTCON.PEIE =3D 1;
 INTCON.GIE  =3D 1;

 T1CON.T1CKPS1 =3D 0;
 T1CON.T1CKPS0 =3D 0;
// T1CON.T1OSCEN =3D 1;
 T1CON.NOT_T1SYNC =3D 1;
 T1CON.TMR1CS  =3D 0;
 T1CON.TMR1ON  =3D 0;

 interrupt_counter =3D 0;
 TMR1H =3D 0;
 TMR1L =3D 0;

 // Esperando final da onda atual
 while(!PORTC.B0);
 while(PORTC.B0);

 // Contagem do tempo necess=E1rio para fechar 32 ciclos
 T1CON.TMR1ON =3D 1;
 while(!PORTC.B0);
 while(PORTC.B0);
 for (x=3D0; x < 30; x++) {
  while(!PORTC.B0);
  while(PORTC.B0);
 }
 while(!PORTC.B0);
 while(PORTC.B0);
 T1CON.TMR1ON =3D 0;

 total =3D ((float)interrupt_counter * 65536) + ((float)TMR1H * 256) +
((float)TMR1L);
 total /=3D 32;
 total =3D 2500000 / total;

 return total;
}

    The idea here is to measure the time it takes to complete 32 cycles,
then divide it by 32 to get the period of one wave. Then divide the numbe=
r
of instructions by second the PIC executes (here 2500000 with a 10MHz clo=
ck)
to get the frequency.

    But this method isn't working very reliably. Someone got a better ide=
a?
Also, I have to implement a timeout on this routine.

    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
-----------------------------------

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