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Dale Stewart
Joined: 21 Apr 2005
Posts: 8
Location: Wollongong, AUSTRALIA
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| Newbie: Timer1 Problem |
 Posted: Fri Jul 15, 2005 9:32 pm |
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Hi
I posted regarding timer0:
http://www.ccsinfo.com/forum/viewtopic.php?t=23653
and now am trying timer1 on 16F876A, 16-bits, prescalar 8 ( maximum for 16F876A ).
According to info from previous post, to send message
"\n\r%u Hello World!." to terminal program on PC, should take around:
( 17 characters * 10 bits/char * 10 lines ) / 9600 bps ~= 177 ms
177ms/4us/tick = 44250 ticks
For timer1 with prescalar 8 (maximum for 16F876A ), on 16F876A overflow should occur
every 262ms
// Timer increments 8000000/(4*8) times per second
// Period = 1/f
// = 1/250000
// = 4 microseconds
// or once every 4 us
// Total # of seconds/overflow:
// = 65536*4E-6
// = 262.144 milliseconds
 When my program executes, I get a really small execution time, suggesting that the timer has overflowed, even though the estimated execution time is within the overflow period.
This happens even when I print only two lines
(17 chars* 10bits/char *2)/9600bps ~= 35 milliseconds.
| Code: |
// This program demonstrates 16-bits timer/counter timer1
// on a 16F876A
#include <16F876A.h>
#fuses NOWDT, NOLVP, HS, PUT, NOPROTECT
#use delay( clock = 8000000 )
#use rs232( baud = 9600, xmit = PIN_C6, rcv = PIN_C7 )
# define INPUT_LINES 10
void main()
{
float time ;
int timer1_ticks, i ;
setup_timer_1( T1_INTERNAL | T1_DIV_BY_8 ) ;
// Timer increments 8000000/(4*8) times per second
// Period = 1/f
// = 1/250000
// = 4 microseconds
// or once every 4 us
// Total # of seconds/overflow:
// = 65536*4E-6
// = 262.144 milliseconds
while ( 1 == 1 )
{
delay_ms( 1000 ) ; // without this, terminal program
// (br@y++) spits out garbage instead of
// text message below
printf( "\n\rPress any key to begin.\n\r" );
getc();
//clear the timer
set_timer1( 0 ) ;
for( i = 1; i <= INPUT_LINES; i++ )
{
printf( "\n\r%u Hello World!.", i ) ;
}
//read the ticks elapsed
timer1_ticks = get_timer1( ) ;
// calculate elapsed time
time = ( 4E-6 ) * timer1_ticks ;
// show the message
printf("\n\rIt took %u timer ticks to print %u lines.", timer1_ticks, INPUT_LINES ) ;
printf("\n\rIt took %4.3e seconds to print %u lines.", time, INPUT_LINES ) ;
}
}
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Output:
| Code: |
Press any key to begin.
1 Hello World!.
2 Hello World!.
3 Hello World!.
4 Hello World!.
5 Hello World!.
6 Hello World!.
7 Hello World!.
8 Hello World!.
9 Hello World!.
10 Hello World!.
It took 167 timer ticks to print 10 lines.
It took 6.680E-04 seconds to print 10 lines.
Press any key to begin. |
Any suggestions most welcome
_________________
:-]
Cheers
Dale |
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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| Posted: Fri Jul 15, 2005 11:30 pm |
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| Quote: | void main()
{
float time ;
int timer1_ticks, i ;
timer1_ticks = get_timer1( ) ; |
In CCS, an "int" is an 8-bit unsigned value. So the problem is
that you're putting a 16-bit value from timer1 into an 8-bit variable. |
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Dale Stewart
Joined: 21 Apr 2005
Posts: 8
Location: Wollongong, AUSTRALIA
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| Posted: Fri Jul 15, 2005 11:50 pm |
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Aha! Cool - that worked!
Thanks PCM for you time and effort. 
That's 2 I owe you! 
_________________
:-]
Cheers
Dale |
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