Help needed with frequency counter

[isaac aiyanyo]

Hi Picstars
i still need your help here as i have being strugling all night with this program.
its the example FREQC.C which is supposed to be a 50mhz frequency counter.
i have ran the program but i am still very confused
with the results i am getting as could understand why parts of the program were commented out?
i want to use it for the frequency range 100Hz to 10Khz
but i am getting the following results

AT 100Hz i get 11000Hz to 12000Hz
AT 1KHz i get about 13870Hz
AT 100KHz i get about 27000Hz
Could someone please tell me where i am going wrong
my program is below
Hope to hear from you soon
Isaac
#if defined(__PCM__)
#include <16F876.H>
#fuses HS,NOWDT,NOPUT,NOPROTECT,NOBROWNOUT,NOLVP
#use delay(clock=20000000)
#use rs232(baud=9600, xmit=PIN_C6, rcv=PIN_C7,RESTART_WDT,ERRORS)
#bit t1_overflow=0x0C.0


// #bit t1_overflow=0xF9E.0 (PIC18, Reminder)

void main() {
int cycles8, cycles;
int32 freq;
long freqc_high;
long freqc_low;

while (TRUE) {
cycles8=0;
cycles=0;
freqc_high=0;
t1_overflow=0;
set_timer1(0);
setup_timer_1(T1_EXTERNAL|T1_DIV_BY_1);
/* ___ wait one second ___ */
while (cycles!=0xFF) { //true=3, false=4
cycles8=0; //1 cycle
//start inner loop
while (cycles8!=0xFF) { //true=3, false=4
if (t1_overflow)//true=2,false=3 //----|
{t1_overflow=0;freqc_high++;}//6 cycles // |
else // |-- 8 cycles
{delay_cycles(5);} //----|
delay_cycles(62); //x
cycles8++; //1
///2 cycles to jump to top
//math: end inner loop
//math: total inner loop=((3+8+x+1+2)*255 + 4)*255
//math: if x=62.87781 then inner loops takes 5mil instructions
//math: if x=62 then inner loop takes 4942920, have to fill 57080 cycles
}
delay_cycles(216); //y
cycles++; ///1 cycle
///2 cylces to jump to top
//math: outer=(3+1+y+1+2)*255+4=57080
//math: y=(57080-4)/255)-(3+1+0+0+1+2)
//math: if y=216.827450980392156862745098039216 then outer loop cylces is 57080
//math: if y=216 then outer loop cycles is off by 211 cycles. z=211
}
delay_cycles(211); //z
/* ___ end waiting 1 second ___ */
setup_timer_1(T1_DISABLED); //turn of counter to prevent corruption while grabbing value
if (t1_overflow) //check one last time for overflow
freqc_high++;
freqc_low=get_timer1(); //get timer1 value as the least sign. 16bits of freq counter
freq=make32(freqc_high,freqc_low); //use new make32 function to join lsb and msb
printf("\%LU Hz\r\n",freq); //and print frequency

}
}
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This message was ported from CCS's old forum
Original Post ID: 13785

[Mark DSylva]

:=Hi Picstars
:=i still need your help here as i have being strugling all night with this program.
:=its the example FREQC.C which is supposed to be a 50mhz frequency counter.

Where does it say that this is a 50Mhz freq. counter? I don't see any reference mentioning that.

:=i have ran the program but i am still very confused
:=with the results i am getting as could understand why parts of the program were commented out?

What parts are commented out? I only see some comments explaining the math, no actual code is commented out!


:=i want to use it for the frequency range 100Hz to 10Khz
:=but i am getting the following results
:=
:=AT 100Hz i get 11000Hz to 12000Hz
:=AT 1KHz i get about 13870Hz
:=AT 100KHz i get about 27000Hz
:=Could someone please tell me where i am going wrong
:=my program is below
:=Hope to hear from you soon
:=Isaac


The code is specifying a 20Mhz clock, is that what you are using?
___________________________
This message was ported from CCS's old forum
Original Post ID: 13787

[isaac aiyanyo]

:=Where does it say that this is a 50Mhz freq. counter? I don't see any reference mentioning that.
<a href="http://www.cc.puv.fi/~t0101190/projekti/source/Examples/ex_freqc.c" TARGET="_blank">http://www.cc.puv.fi/~t0101190/projekti/source/Examples/ex_freqc.c</a>
:=What parts are commented out? I only see some comments explaining the math, no actual code is commented out!
Yes you were right there sorry for the mislead
its all to do with my C knowlegde

:=The code is specifying a 20Mhz clock, is that what you are using?
i am using a 20Mhz clock.

Please help
Isaac
___________________________
This message was ported from CCS's old forum
Original Post ID: 13789