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zeronix
Joined: 08 Jun 2010
Posts: 9
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| Interrupt problem in pic 18f2550 with usb bootloader |
 Posted: Wed Jun 09, 2010 2:29 pm |
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Hi .. I'm trying to fire an interrupt with timer 0 in my PIC 18f2550 but I'm not being successful.
I'm trying initial to flash an led with 1 second delay. I'm using an bootloader to program the pic with the c code and I'm using an external crystal with 20MHz.
I do the following calculations: Tout=1 sec, so Fout=1Hz
(20000000/4)/128 =39062/256 =152,58 approx = 153
I'm using this code:
| Code: |
#include <18f2550.h>
#fuses HSPLL,NOWDT,NOBROWNOUT,NOPROTECT,NOLVP,NODEBUG,USBDIV,PLL5,CPUDIV1,VREGEN,MCLR,NOPBADEN,WRTB,CPB
#use delay(clock=48000000)
#use RS232(baud=9600, parity=N, bits=8, xmit=PIN_C6,rcv=PIN_C7) // configura serial
// serial configurada para velocidade de 9600 bps
// sem paridade, 8 bits
#build(reset=0x800, interrupt=0x808)
#org 0x000, 0x7ff { }
#define LED1 PIN_C0
#define LED2 PIN_C1
#define LED3 PIN_C2
#define HIGH_START 153
byte seconds, high_count;
#int_timer0
clock_isr() {
if(--high_count==0) {
// printf("test2");
output_high(LED1);
delay_us(5);
output_low(LED1);
high_count=HIGH_START;
}
}
main() {
high_count=HIGH_START;
set_timer0(0);
setup_timer_0(RTCC_EXT_H_TO_L | RTCC_DIV_128 | RTCC_8_BIT);
enable_interrupts(INT_TIMER0);
enable_interrupts(GLOBAL);
//output_high(LED1);
printf("test2");
while(TRUE);
}
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Anyone have an idea where is the problem? Thanks in advance. |
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mkuang
Joined: 14 Dec 2007
Posts: 257
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| Posted: Wed Jun 09, 2010 2:32 pm |
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| How do you get 48Mhz from an external crystal of 20 Mhz? Make sure you are setting the right pre-scaler values for the external clock (page 31 of the datasheet). |
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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| Posted: Wed Jun 09, 2010 2:45 pm |
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The PIC will be running at 48 MHz, due to the PLL being used.
The PLL5 fuse divides the 20 MHz down to 4 MHz, which is required
by the PLL. The PLL then generates 96 MHz, which is divided down
to 48 MHz to run the PIC.
See the sample programs in this thread below, which show how to run
the PIC at 20 MHz, and at 48 MHz. For USB, you should use 48 MHz.
http://www.ccsinfo.com/forum/viewtopic.php?t=42223&start=1
Note: You are already running it at 48 MHz in your posted code. |
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zeronix
Joined: 08 Jun 2010
Posts: 9
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| Posted: Wed Jun 09, 2010 3:09 pm |
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| PCM programmer wrote: | The PIC will be running at 48 MHz, due to the PLL being used.
The PLL5 fuse divides the 20 MHz down to 4 MHz, which is required
by the PLL. The PLL then generates 96 MHz, which is divided down
to 48 MHz to run the PIC.
See the sample programs in this thread below, which show how to run
the PIC at 20 MHz, and at 48 MHz. For USB, you should use 48 MHz.
http://www.ccsinfo.com/forum/viewtopic.php?t=42223&start=1
Note: You are already running it at 48 MHz in your posted code. |
hi PCM , but im in setup_timer_0(RTCC_EXT_H_TO_L | RTCC_DIV_128 | RTCC_8_BIT); use the 20mhz external oscilator.. isnt that fine for my counts? |
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zeronix
Joined: 08 Jun 2010
Posts: 9
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| Posted: Wed Jun 09, 2010 3:13 pm |
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| mkuang wrote: | | How do you get 48Mhz from an external crystal of 20 Mhz? Make sure you are setting the right pre-scaler values for the external clock (page 31 of the datasheet). |
Hi, I think I'm using the correct pll and cpudiv for 20 mhz input oscillator. I already use this pic to obtain x,y,z accelerometer values but with no timer, only with a simple function with no accuracy in time. I already verify that in page 32. |
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