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seanyGood
Joined: 07 Jan 2004
Posts: 3
Location: Fresno, Ca
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| timer 0 help |
 Posted: Wed Jan 07, 2004 6:34 pm |
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Hi everybody,
I am new to using timers on the PIC, and i am having a little trouble. I am using a PIC 16F877 (on the MP-LAB ICD demo board) and an 8 Mhz clock. I want the timer 0 interrupt to occur every 10 ms. So here are my calculations: 8000000/(4*128) == 15625 increments per second. So (15625 increments)/(1 second) == (X increments)/(10*10^-3 seconds).
Solve for X, and that gives me 156.25 increments/10ms. So in order to get 156 increments before overflow, i use the statement
set_rtcc(100);
Anyways, i set up a little test program to see if i was correct, and apparently i am missing something. I set up a counter in the timer0 interrupt, and so when the counter reaches 500, that should be 5 seconds, when it reaches 1500 that should be 15 seconds and so on. In the 5 second case, the actual time it is taking is 8.5 seconds. In the 15 second case the actual time it is taking is 25 seconds. So I will post my code below in case the problem can't be found in my above calculations. Thanks for any help you can give!
| Code: |
/************************
* includes
************************/
#include <16F877.h> /* device file for demo board use */
/************************
* directives
************************/
//DEBUG remove unnecessary fuses after testing
#fuses XT, \
NOWDT, \
NOPROTECT, \
NOLVP, \
DEBUG
#use delay (clock=8000000) //DEBUG Use with Microchip ICD demo board
/************************
* enumerations
************************/
enum ADU_STATES
{
STATE_LED_OUTPUT,
STATE_ADU_STATE_MAX
};
/************************
* prototypes
************************/
void initialize();
void timeInit();
void LED_Output();
#int_rtcc
void ISRmbTimer();
/************************
* constants
************************/
/*LED output pins */
#define CRITICAL_LED_PIN PIN_C2 /* 17 */
#define MAJOR_LED_PIN PIN_C1 /* 16 */
#define MINOR_LED_PIN PIN_C0 /* 15 */
/* Times in 10 ms increments */
#define TIME_ONE 500 // 5 seconds
#define TIME_TWO 1500 // 15 seconds
#define TIME_THREE 4500 // 45 seconds
/************************
* globals
************************/
ADU_STATES progState;
int32 timeCounter;
#int_rtcc
void ISRmbTimer()
{
timeCounter++;
}
void timeInit()
{
int8 i;
timeCounter = 0;
/* set real-time clock counter to interrupt every 10ms */
setup_timer_0(RTCC_INTERNAL|RTCC_DIV_128);
set_rtcc(100);
enable_interrupts(int_timer0);
enable_interrupts(GLOBAL);
progState = STATE_LED_OUTPUT;
}
void LED_Output()
{
if (timeCounter > TIME_THREE)
{
output_High(CRITICAL_LED_PIN);
}
else
{
output_Low(CRITICAL_LED_PIN);
}
if (timeCounter > TIME_TWO)
{
output_High(MAJOR_LED_PIN);
}
else
{
output_Low(MAJOR_LED_PIN);
}
if (timeCounter > TIME_ONE)
{
output_High(MINOR_LED_PIN);
}
else
{
output_Low(MINOR_LED_PIN);
}
progState = STATE_LED_OUTPUT;
}
void main()
{
timeInit();
while (true)
{
switch(progState)
{
case STATE_LED_OUTPUT:
LED_Output();
break;
default:
}
}
}
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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| Posted: Wed Jan 07, 2004 7:15 pm |
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| Quote: | Anyways, i set up a little test program to see if i was correct,
and apparently i am missing something. |
The RTCC does not automatically reload itself with the preset value.
You have to do it the isr. See the CCS examples, EX_SINE.C and
EX_DTMF.C. |
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seanyGood
Joined: 07 Jan 2004
Posts: 3
Location: Fresno, Ca
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| timer 0 help |
| Posted: Wed Jan 07, 2004 7:47 pm |
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| Right on the money PCM Programmer. Thanks. |
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