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Amend
Joined: 08 Mar 2021
Posts: 3
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| PWM as an input to another digital input pin |
 Posted: Mon Mar 08, 2021 8:47 pm |
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Hi,
I'm trying to set the PWM signal generated by the CCP1 pin in the PIC16F887 as an input to the PIN_A4, in order to then use it as an output of different pins of ports B and D.
I'm using CCS Compiler and I've read the manual, however I can't get the pins of ports B and D to output the same frequency as the PWM signal (2.5kHz) input in A4, as for now, the output of those ports are HIGHs and LOWs with a frequency of 1-2Hz.
| Code: | #include <16f887.h>
#fuses XT,NOWDT,NOPROTECT,NOLVP,PUT,BROWNOUT,INTRC_IO
#use delay(clock=4M)
#byte PORTA=0x05
#byte PORTB=0x06
#byte PORTD=0x08
#byte TRISA=0x85
#byte TRISB=0x86
#byte TRISD=0x88
void main() {
TRISA=0b00001111;
TRISB=0;
TRISD=0;
PORTA=1;
PORTB=0;
PORTD=0;
//To set the PWM with a f=2500Hz:
//PWM = (PR2+1) * 4 * TOsc * Preescaler
//PR2= PWM / (4 * Preescaler * TOsc) -1
//= 0.0004/ (4 * 4 * 0.000000250) -1
//PR2=99
Timer2=99;
Poscaler=1;
setup_timer_2(t2_div_by_4,Timer2,Poscaler);
setup_ccp1(ccp_pwm); //CCP1 as PWM
//duty cycle = (PR2+1)(4)
//=(99+1)*4
//=400
//400 --> 100%
// x --> 50%, x=200
set_pwm1_duty((int16)200);
while(true){
if(input(PIN_A0)==0 && (input(PIN_A1))==0 && (input(PIN_A2))==0
&& (input(PIN_A3))==0){
delay_ms(300);
output_bit(PIN_B0, input(PIN_A4));
}
else{
output_low(PIN_B0);
}
if(input(PIN_A0)==0 && (input(PIN_A1))==0 && (input(PIN_A2))==1
&& (input(PIN_A3))==0){
delay_ms(300);
output_bit(PIN_B1, input(PIN_A4));
}
else{
output_low(PIN_B1);
}
}
} |
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alan
Joined: 12 Nov 2012
Posts: 349
Location: South Africa
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| Posted: Mon Mar 08, 2021 11:58 pm |
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| Well 1st glaring problem are the 2 delay_ms(300), which will result in a freq of approx 1.6Hz if you just toggle the 2 pins. |
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temtronic
Joined: 01 Jul 2010
Posts: 9102
Location: Greensville,Ontario
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| Posted: Tue Mar 09, 2021 8:11 am |
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hmm... from another website....
| Quote: |
//Timer2
//Prescaler 1:1; Postscaler 1:2; TMR2 Preload = 199; Actual Interrupt Time : 400 us |
Might be worth checking the 'math'.
Also is this a real PIC and NOT a 'simulation' ?
If real, did you compile in 'debug' or 'release' mode (if using MPLAB). |
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Ttelmah
Joined: 11 Mar 2010
Posts: 19219
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| Posted: Tue Mar 09, 2021 8:39 am |
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His PWM maths is right. As Alan points out, it It is just that he is sampling
the input signal only once every 300mSec. Result very slow actual update...
The figure you were looking at was for an interrupt rate from the timer
not a PWM. Since there is no postscaler when used as a PWM... |
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Amend
Joined: 08 Mar 2021
Posts: 3
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| Posted: Wed Mar 10, 2021 10:29 am |
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| alan wrote: | | Well 1st glaring problem are the 2 delay_ms(300), which will result in a freq of approx 1.6Hz if you just toggle the 2 pins. |
Thank you Alan, you were right, the delay was causing problems. By removing it the signal comes out right now! |
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Amend
Joined: 08 Mar 2021
Posts: 3
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| Posted: Wed Mar 10, 2021 10:30 am |
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| Ttelmah wrote: | His PWM maths is right. As Alan points out, it It is just that he is sampling
the input signal only once every 300mSec. Result very slow actual update...
The figure you were looking at was for an interrupt rate from the timer
not a PWM. Since there is no postscaler when used as a PWM... |
You're right, I removed the delay and now the signal is accurate. Thank you very much |
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