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Fabri
Joined: 22 Aug 2005
Posts: 275
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| Different PWM frequency in PIC18F67K22 |
 Posted: Sat May 21, 2016 1:32 am |
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Dear All,
I use PIC18F46K22 (CCS V4.135) with timer 2 for PWM1 4Khz as follow
| Code: |
setup_timer_2(T2_DIV_BY_16, 2000, 1);
set_pwm1_duty(100);
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Now I need to have second PWM with PWM3 with different frequency:
| Code: |
SETUP_CCP3(CCP_USE_TIMER3_AND_TIMER8);
setup_timer_3(T3_DIV_BY_2);
setup_timer_8(T8_DIV_BY_16, 100, 1);
SETUP_CCP3(CCP_PWM );
set_pwm3_duty(100);
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I have always 4Khz PWM3 so can somebody suggest me solution to have different frequency in PWM3 ?
Thanks, |
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Ttelmah
Joined: 11 Mar 2010
Posts: 19505
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| Posted: Sat May 21, 2016 2:50 am |
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You don't tell us your clock rate?.
However I'm surprised you get the frequency you expect with your timer2 setup.
The period register for timer2, is an 8bit register. Can't take '2000'. Should be accepting probably the low byte of the value you are giving, so 0xD0 (209 counts).
Then the big problem is that setup_ccp calls are not 'cumulative'. Your second setup_ccp call (CCP_PWM), turns off the timer selection setting.
Now, puzzled by your "CCP_USE_TIMER3_AND_TIMER8"
You need to read the data sheet. CCP3 defaults to using timer1 for capture and timer 2 for PWM. You then have modes that can switch it to using timer4, or timer 6 for PWM. I've loaded 4.135, and the defines available, are:
| Code: | #define CCP_USE_TIMER1_AND_TIMER2 0x0000
#define CCP_USE_TIMER3_AND_TIMER4 0x0100
#define CCP_USE_TIMER5_AND_TIMER6 0x0200
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Then read the note above this in the file. Note that it says the first is for compare, and the second for PWM.
So you need (assuming timer 6):
| Code: |
SETUP_CCP3(CCP_USE_TIMER3_AND_TIMER6 | CCP_PWM);
setup_timer_6(T6_DIV_BY_16, 100, 1);
set_pwm3_duty(50);
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It does tell you in the include file:
"or (via |) together constants from each group"
Since you are using PWM, timer3 doesn't enter the equation at all.
Then (of course) since the PWM time constant is now 101 (always one greater than the value in the PR2 register), the duty cycle settings needs to be approximately half this for a near square wave. |
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Fabri
Joined: 22 Aug 2005
Posts: 275
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| Posted: Mon May 23, 2016 9:39 am |
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Thanks Ttelmah for your Help.
Clock Rate is 64 Mhz because I must use PLL in this application.
I tryed as you suggested me and I have a 9 Khz PWM in CCP3.
Now I have to work around to have 1 Khz PWM
Regards,
Fabri |
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Ttelmah
Joined: 11 Mar 2010
Posts: 19505
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| Posted: Mon May 23, 2016 10:06 am |
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From 64MHz you can't do it.
The maximum division available is 4*16*255 = 16384
This gives 3.906KHz.
Normally you want PWM's to be fast. The hardware is designed to do this.
You could generate a timer based square wave, by just using an interrupt at 2KHz, or using a CCP to handle the actual pin. |
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Fabri
Joined: 22 Aug 2005
Posts: 275
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| Posted: Mon May 23, 2016 10:31 am |
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Yes, I'm working on now and I understand limit of my clock rate.
I'll work with firmware to have 1Khz pwm.
Regards, |
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Ttelmah
Joined: 11 Mar 2010
Posts: 19505
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| Posted: Mon May 23, 2016 11:10 am |
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Why do you need this frequency?.
What does the PWM resolution need to be?. |
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Ttelmah
Joined: 11 Mar 2010
Posts: 19505
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| Posted: Mon May 23, 2016 11:38 am |
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Have a look at this thread.
<http://www.ccsinfo.com/forum/viewtopic.php?t=50914&highlight=ccp>
I post code here for a 400Hz CCP based PWM, that can possibly be modified for your needs. |
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Fabri
Joined: 22 Aug 2005
Posts: 275
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| Posted: Mon May 23, 2016 1:44 pm |
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Thanks for new suggestion, I'll check that post.
Regards, |
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