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filjoa
Joined: 04 May 2008
Posts: 260
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| timer2 period program |
 Posted: Tue Sep 14, 2010 8:57 am |
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hi
I need have an interrupt every 12.4ms, for that I try program timer1 but i don't know how I can make that manually...
I use CCS wizard and it program this "setup_timer_2(T2_DIV_BY_16,242,16);"
Is correct? every 12.4ms I have an call to timer1 routine?
What is formula to program timer manually?
Is possible use timer1 to have an interrupt every 12.4ms?
best regards |
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Geps
Joined: 05 Jul 2010
Posts: 129
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| Posted: Tue Sep 14, 2010 9:30 am |
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| Which PIC and crystal combination are you using? |
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filjoa
Joined: 04 May 2008
Posts: 260
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| Posted: Tue Sep 14, 2010 12:27 pm |
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hi
sorry....
PIC18F252 with crystal 20Mhz
best regards |
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Ttelmah
Joined: 11 Mar 2010
Posts: 19544
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| Posted: Tue Sep 14, 2010 1:20 pm |
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Master clock/4
Divide by prescaler (/16).
Divide by second value+1 (/243)
Divide by postscaler (/16).
So interrupt frequency in your case, is 20000000/(4*16*243*16) = 80.37Hz
1/80.37=0.0124416
12.4416mSec
To calculate for yourself, work the other way.
1/0.0124=80.645
5000000/80.645 = 62000 (master clock is divided by 4)
So the prescaler*postscaler*(count+1) needs to be 62000.
However you have limited values for all the values (data sheet), so the automatic values look to be as close as possible.
Rermember it is the timer2 interrupt that is called (you refer to timer1....).
Best Wishes |
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filjoa
Joined: 04 May 2008
Posts: 260
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| Posted: Tue Sep 14, 2010 3:34 pm |
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hi
Thanks for this excellent explanation...
Where I can find more information like that to calculate timer0, timer1 and timer3?
Best regards |
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filjoa
Joined: 04 May 2008
Posts: 260
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| Posted: Thu Sep 16, 2010 4:55 pm |
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Hi
I need join on my program other pulse with 12.4ms, so I need use other timer, for example timer1...
What is process for I can calculate timer1 with 12.4ms?
best regards |
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filjoa
Joined: 04 May 2008
Posts: 260
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| Posted: Thu Sep 16, 2010 7:21 pm |
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Hi
I read read CCS manual but I can get one way to make timer1 with interrupts every 12.4ms....
Someone can explain me?
best regards |
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filjoa
Joined: 04 May 2008
Posts: 260
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| Posted: Thu Sep 16, 2010 7:37 pm |
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Hi
Sorry for my insistence.
If I have my timers 1 and 2 configured like that:
| Code: |
enable_interrupts(GLOBAL);
enable_interrupts(INT_TIMER1);
setup_timer_1(T1_INTERNAL | T1_DIV_BY_8); // periodo de 12.4ms
set_timer1(7750);
enable_interrupts(INT_TIMER2);
setup_timer_2(T2_DIV_BY_16,242,16); // periodo de 12.4ms
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For timer1 to generate an interrupt every 12.4ms I add "set_timer1(7750)".
This stay correct?
I have two pulses with different timers?
best regards |
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Ttelmah
Joined: 11 Mar 2010
Posts: 19544
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| Posted: Fri Sep 17, 2010 3:50 am |
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Seriously, _read the data sheet_.
The timer operation, is nothing to do with CCS. It varies between different chips. The 'bible' for this, is the data sheet of the chip, which tells you where the clock can come from, what pre-scalers, post-scalers, and division ratios are available.
There is also an application note on the Microchip site, giving an 'overview' of configuring/using the timers, on a 'mid range' PIC, and most of this applies to the other families as well.
Best Wishes |
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filjoa
Joined: 04 May 2008
Posts: 260
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| Posted: Mon Oct 18, 2010 9:32 am |
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Hi
I need program my timers during program run but I don't know how I can configure timer2.
My actual configuration:
| Code: |
setup_timer_1(T1_INTERNAL | T1_DIV_BY_1); // periodo de 13.1ms
enable_interrupts(INT_TIMER1);
setup_timer_2(T2_DIV_BY_16,243,16); // periodo de 12.4ms
enable_interrupts(INT_TIMER2);
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On timer1 routine I need configure it to 1ms and I make this:
65535 - (1ms/(4/20Mhz))
and put result on set_timer1(xxxx);
But I don't know how I can make this to timer2...
Someone can help?
best regards |
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Humberto
Joined: 08 Sep 2003
Posts: 1215
Location: Buenos Aires, La Reina del Plata
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| Posted: Mon Oct 18, 2010 12:57 pm |
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Thelmah gave you a practical way regarding how to calculate the interrupt period, sorry I do not understand
what is your real problem right now:
- the timer do not behave as you expected.
- the timer is rolling back but the time is not the expected.
- the timer is rolling back but the interrupt is not generated.
I would like to know how are you testing the timers code, in real hardware or in a simulator way.
Please read this thread:
http://www.ccsinfo.com/forum/viewtopic.php?t=22467&highlight=timers
Regards |
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MiniMe
Joined: 17 Nov 2009
Posts: 50
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| Posted: Mon Oct 18, 2010 2:55 pm |
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You can use application with nice user interface to have a idea about effect of different values (prescalers, counters, exact time values... )
http://pictimer.picbingo.com/ |
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filjoa
Joined: 04 May 2008
Posts: 260
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| Posted: Mon Oct 18, 2010 3:05 pm |
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hi
Thanks for sugestion...
I find on CCS manual and formula is: 256 - (temp/(4/clock)) without prescale...
But I use prescale and postscale... setup_timer_2(T2_DIV_BY_16,242,16);
Is correct I make this calcs: 256 - (temp /((242*4)/20Mhz))
Or I need change 256 to 242? or need make other thing?
Or stay wrong? |
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Humberto
Joined: 08 Sep 2003
Posts: 1215
Location: Buenos Aires, La Reina del Plata
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| Posted: Mon Oct 18, 2010 4:20 pm |
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| Quote: |
Or I need change 256 to 242? or need make other thing?
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It depends of the interrupt handler overhead, this value is used to fine trim the period in your real application.
Thats why it is important to know 'how' are you testing your project.
Regards |
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filjoa
Joined: 04 May 2008
Posts: 260
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| Posted: Mon Oct 18, 2010 4:37 pm |
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You can see my timer configuration and I think which my timer only go at 242.
So on my formula I think correct use 242 to subtract or I need use always "256 - (temp......"?
I need this configuration to generate pulses...
| Code: |
#int_TIMER1
void TIMER1_isr(void)
{
if (!pause_cycle)
{
output_high(S1SP);
set_timer1(57535); //1.6ms -->> 65535 - (1.6ms/(4/20Mhz))
pause_cycle = 1;
} else
{
output_low(S1SP);
pause_cycle = 0;
}
}
#int_TIMER2
void TIMER2isr(void)
{
if (!pause_cycle)
{
output_high(S2DR);
[b]set_timer2(???????); //1.4ms --->> 242 - (temp /((242*4)/20Mhz)) ???[/b]
pause_cycle = 1;
} else
{
output_low(S2DR);
pause_cycle = 0;
}
}
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How I can make timer2 pulse with 1.4ms???
best regards |
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