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pilar
Joined: 30 Jan 2008
Posts: 197
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| Question about timer0 |
 Posted: Wed Jan 13, 2010 8:29 am |
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Hi, am working with a Pic16f88 to 20MHz, someone please can tell me what means ?
| Code: | | setup_timer_0(RTCC_INTERNAL | RTCC_DIV_2); |
and what is the formula to get the value of Periodo to place in | Code: | | set_timer0(Periodo); |
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mkuang
Joined: 14 Dec 2007
Posts: 257
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| Posted: Wed Jan 13, 2010 9:26 am |
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It means you are using the MCU clock for timer0 and using a divider of 2. Timer0 can be operated in either 8 or 16 bit mode in most(?) 16 or 18 series PICS (check the datasheet). The basic tick is (Fosc/4/divider) in frequency so if your Fosc = 20M your basic timer0 tick lasts 0.4 us in duration. In 8 bit mode timer0 counts from whatever value you set it to up to 255 so the total time is 0.4us*(255 - set_value). In 16 bit mode the total time is 0.4us*(65525- set_value). So if you know how long you want your period to be you can just use do:
| Code: |
set_timer0(set_value);
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where set_value is int8 for 8 bit mode and int16 for 16 bit mode. |
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Guest
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| Posted: Mon Jan 18, 2010 10:26 am |
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Hi, I am use a pic16f88 to 20MHz and I am use the detector RB0/Int pin to detect the Zero crossing, like I need short pulses each half cycle for that I am use the INT_TIMER0, my problem is that the pulses are outdated and do not correspond to 8.33ms as this made the calculation.
Someone can help me?
| Code: | #include <16F88.h>
#fuses HS,NOWDT,NOPUT,NOLVP,NOBROWNOUT,NOCPD,NOWRT,NODEBUG
#use delay(clock=20000000)
#use fast_io(A)
#use fast_io(B)
#byte PORTA = 0x05
#byte PORTB = 0x06
#bit LED_ROJO = PORTA.2
#byte ANSEL = 0x9B
#byte OPTIONREG = 0x81
#define Semi_Ciclo 156
int Contador;
int i,j;
#INT_TIMER0
void tempo0(){
Contador++;
if (Contador == 208){
LED_ROJO=1;
Delay_us(20);
LED_ROJO=0;
Contador = 0;
}
}
#INT_EXT
void CrucePor0()
{
set_timer0(Semi_ciclo);
if (j==0){
j=1;
ext_int_edge(H_TO_L);
}
else {
j=0;
ext_int_edge(L_TO_H);
}
}
void main()
{
set_tris_B(0b11001101);
set_tris_A(0b00011000);
ANSEL=0;
OPTIONREG=OPTIONREG & 0x7F;
setup_timer_0(RTCC_INTERNAL | RTCC_DIV_2);
enable_interrupts(INT_TIMER0);
enable_interrupts(INT_EXT);
ext_int_edge(L_TO_H);
enable_interrupts(GLOBAL);
set_timer0(Semi_ciclo);
while(1);
}
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