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ve4edj
Joined: 08 May 2014
Posts: 3
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| 0% PWM issue on 16F1827 - [SOLVED] |
 Posted: Thu May 08, 2014 9:27 am |
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I am trying to fade LEDs connected to a PIC16F1827 on and off based on a time read from a RTC chip (MCP79410). But at the moment, I am having an issue with 0% PWM not turning the LED off (it gets fairly dim, but is NOT off)
My setup code:
| Code: | void initPWMs() {
setup_ccp2(CCP_PWM);
set_pwm2_duty(0);
setup_ccp3(CCP_PWM);
set_pwm3_duty(0);
setup_ccp4(CCP_PWM);
set_pwm4_duty(0);
setup_timer_2(T2_DIV_BY_4, 100, 1);
APFCON0 |= 0x08;
}
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At this point all three LEDs are off. However, after adding this code:
| Code: | if (seconds % 2 == 0) {
set_pwm2_duty(1023);
set_pwm3_duty(0);
} else {
set_pwm2_duty(0);
set_pwm3_duty(1023);
}
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The LEDs alternate between very bright and kind of dim every second. Can anybody shed some light on this issue? Thanks in advance!
--- EDIT ---
Forgot to mention the compiler version I am using. I'm on v5.023
Last edited by ve4edj on Thu May 08, 2014 10:11 am; edited 1 time in total |
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stinky
Joined: 05 Mar 2012
Posts: 99
Location: Central Illinois
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| Posted: Thu May 08, 2014 10:02 am |
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Don't remember if this is well documented in the manual. The PWM is 10 bit in this family. set_pwmx_duty(0) only clears the MSB of the duty register. The lower two bits could still be hi. Check your datasheet.
Fix With Cast:
| Code: | set_pwm2_duty(0L);
002C: MOVLB 05
002D: CLRF CCPR2L
002E: MOVF CCP2CON,W
002F: ANDLW CF
0030: MOVWF CCP2CON
0031: GOTO 02D |
| Code: | set_pwm2_duty(0);
002C: MOVLB 05
002D: CLRF CCPR2L
002E: GOTO 02D |
Explicitly casting it as a long will get the compiler to address the two lowest bits in the duty register. |
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ve4edj
Joined: 08 May 2014
Posts: 3
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| Posted: Thu May 08, 2014 10:04 am |
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| stinky wrote: | Don't remember if this is well documented in the manual. The PWM is 10 bit in this family. set_pwmx_duty(0) only clears the MSB of the duty register. The lower two bits could still be hi. Check your datasheet.
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I must have read through that manual 50 times, and I'm almost sure that is mentioned nowhere. Thanks for the prompt reply, I'll try it out and let you know!  |
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ve4edj
Joined: 08 May 2014
Posts: 3
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| Posted: Thu May 08, 2014 10:10 am |
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| Problem solved. Thanks @stinky!!! |
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