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Demetrius
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| Timer1 count too fast |
 Posted: Wed Apr 22, 2009 4:29 pm |
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I used an LC circuit with a comparator to generate a square ware, and measure the frequency.
I want to use the 16 bit Timer1 as counter, but it seems to count too fast.
| Code: | #include <16F876A.h>
#device adc=8
#FUSES NOWDT //No Watch Dog Timer
#FUSES HS //High speed Osc (> 4mhz for PCM/PCH) (>10mhz for PCD)
#FUSES NOPUT //No Power Up Timer
#FUSES NOPROTECT //Code not protected from reading
#FUSES NODEBUG //No Debug mode for ICD
#FUSES NOBROWNOUT //No brownout reset
#FUSES NOLVP //No low voltage prgming, B3(PIC16) or B5(PIC18) used for I/O
#FUSES NOCPD //No EE protection
#FUSES NOWRT //Program memory not write protected
#use delay(clock=20000000)
#include "lcd.c"
void main()
{
setup_adc_ports(NO_ANALOGS);
setup_adc(ADC_OFF);
setup_spi(SPI_SS_DISABLED);
setup_timer_0(RTCC_EXT_L_TO_H|RTCC_DIV_1);
setup_timer_1(T1_EXTERNAL_SYNC|T1_DIV_BY_1);
//setup_timer_1(T1_EXTERNAL|T1_DIV_BY_1);
setup_timer_2(T2_DISABLED,0,1);
setup_comparator(A0_A3_NC_NC_OUT_ON_A4);
setup_vref(FALSE);
lcd_init();
printf(lcd_putc,"\f init");
while(true) {
input(PIN_C6); // open gate
set_timer0(0);
set_timer1(0);
delay_ms(100);
output_high(PIN_C6); // close gate
printf(lcd_putc,"\fT1: %Lu",get_timer1());
printf(lcd_putc,"\nT0: %u",get_timer0());
}
}
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C6 is connected to C0/T1CKI and A4/T0CKI
On Timer0 I get correct count (226) but I want to increase the frequency and use a 16bit counter. On Timer1 instead I get a value that varies (apparently) randomly between 320-360.
I tried also to enable/disable timer before/after reading and writing value to timer register, and I tried also setup_timer_1(T1_EXTERNAL|T1_DIV_BY_1);
but with no luck.
Thanks for any help! |
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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| Posted: Wed Apr 22, 2009 4:50 pm |
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| Quote: | while(true) {
input(PIN_C6); // open gate
set_timer0(0);
set_timer1(0);
delay_ms(100);
output_high(PIN_C6); // close gate
printf(lcd_putc,"\fT1: %Lu",get_timer1());
printf(lcd_putc,"\nT0: %u",get_timer0());
} |
The input() function sets the TRIS for pin C6 to be an input.
Do you have a pull-up or pull-down resistor on that pin ?
If you don't have one of those on it, the pin will be a "floating" input.
Why did you set it to be an input ?
Also, you have a while() loop to create your pulses, but then you have
printf statements inside the loop. The printf statements will take a
variable amount of time, depending upon how many digits they have
to display. |
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Demetrius
Guest
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| Posted: Wed Apr 22, 2009 7:13 pm |
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No, i don't generate any pulses with the code.
I want to measure the frequency of a square ware counting the rising front of the signal.
C6 is connected with the pin C0/T1CKI and the signal source (it don't remain floating).
I set C6 as input and the signal go into it and the C0/T1CKI (timer1 counter pin). After 100ms, I set the C6 as output, so at the C0/T1CKI there is a constant value and the timer dont' increment.
I read the timer value and display it on lcd.
With Timer0 this work correctly, with timer1 no. |
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