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GDetienne
Joined: 20 Sep 2003
Posts: 47
Location: Brussel - Belgium
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| Question about Timer 1. |
 Posted: Fri Jun 03, 2005 10:18 am |
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I use a 16F876A and PCWM 3.217. I want to use the timer1 to count the time in msec.
At each timer1 interrupt, I reset it with (65536-4000) to count 1 msec and I increment the mseccount.
My pic receive also one pulse each second (accuracy of 1 µSec) on B0.
During this interrupt, I reset the timer1, set a flag, copy mseccount to mseccountold and set msecount to 0.
In the main I print the mseccountold value.
My projet use 92 % of the space.
When I run it, I see that between two pulses on B0, the counter have 993 mSec.
Now I write a little program (see below) with only both interrupts. The output give 995 msec.
My questions are :
- why not 1000 msec ?
- why 2 msec difference, time in bank switching ?
| Code: |
#include <16F876A.h>
#device *=16
#use delay(clock=16000000)
#define CRYSTAL_FREQ 16000000
#fuses HS,NOWDT,PUT,BROWNOUT,NOWRT,NOLVP
#use rs232 (baud=9600,parity=N,xmit=PIN_C6,rcv=PIN_C7,stream=PC,errors)
#define timer1init 61536 // (65536 - 4000)
#use fast_io ( A )
#use fast_io ( B )
#use fast_io ( C )
#priority EXT , TIMER1
static long lmSecCount, lmSecCountOld;
static char Pulse;
/**** Interrupts ******************************************/
#INT_TIMER1
void Timer1Interrupt ( void )
{
set_timer1(timer1init+get_timer1());
lmSecCount ++;
output_toggle(PIN_A1);
}
#int_ext
// Pulse on B0
void intRB0 ()
{
set_timer1(timer1init);
lmSecCountOld = lmSecCount;
lmSecCount=0;
Pulse = 1;
}
/* Main */
void main ( void )
{
/* INITIALIZE */
port_b_pullups(TRUE);
setup_adc_ports ( NO_ANALOGS );
set_tris_b(0xff);
set_tris_a(0x20);
set_tris_c(0b10011010);
setup_timer_1(T1_INTERNAL ||T1_DIV_BY_1);
set_timer1(timer1init);
/* INTERRUPTS */
Pulse = 0 ;
enable_interrupts ( INT_EXT ); // PPS interrupt
enable_interrupts (INT_TIMER1); // enable timer1 interrupts
enable_interrupts ( GLOBAL ); // enable all interrupts
/* MAIN LOOP */
while ( TRUE )
{
if (Pulse == 1)
{
fprintf(PC,"%04lu ",lmSecCountOld);
Pulse = 0;
}
}
} |
If somebody can put me on the correct way. Thanks in advance. |
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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| Posted: Fri Jun 03, 2005 11:09 am |
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In this thread, Mark and ckielstra recommend against the method of
adding the current timer value to the constant, and instead they suggest
that you should just tweak the constant value so it works.
This thread is about Timer0, but the same idea applies to Timer1.
http://www.ccsinfo.com/forum/viewtopic.php?t=21573&start=0 |
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GDetienne
Joined: 20 Sep 2003
Posts: 47
Location: Brussel - Belgium
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| Posted: Sat Jun 04, 2005 9:10 am |
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Many thanks for your answer.
You are right, the instruction "set_timer1(timer1init+get_timer1());" ask 21 instructions. During this time I loss minimum 5 µSec.
Do you think it's possible to reduce this code ?
Thanks a lot, have a nice week end. |
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Mark
Joined: 07 Sep 2003
Posts: 2838
Location: Atlanta, GA
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| Posted: Sat Jun 04, 2005 10:14 am |
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If you use timer2, you won't have to reload the value.
You could use the CCP module in compare mode as well. You can either set it to reset on match or you could just keeping adding the value to the ccp register. |
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GDetienne
Joined: 20 Sep 2003
Posts: 47
Location: Brussel - Belgium
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| Thanks |
| Posted: Sat Jun 04, 2005 3:01 pm |
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Thanks Mark and PCM programmer for your help.
I try in this way.
Have a nice week end. |
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