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PIC16F1826 output voltage unstable

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Hey guys,

I am developing a project with the PIC16F1826 and one of my outputs is flotoating like 1.9V, 2.9V and I can´t find why. I already check the ANSEL registers and initialize the PORTs at 0. It start´s when I add more if statements in my checkmodule() function...

Here is the code:

int c=0;

int c1_m1 = 0;

int c1_m2 = 0;

int c1_m3 = 0;

void main(){

OSCCON = 0b01110000;

ANSELA = 0b00000000;

ANSELB = 0b00000000;

TRISA=0b11111111;

PORTA = 0b00000000;

TRISB=0b00000000;

PORTB = 0b00000000;

while(1){

checkmodules();

module_status();

}

}

void checkmodules(){

if(PORTAbits.RA1==1){

if(c1_m1==0){

c++;

c1_m1=1;

}

}

if(PORTAbits.RA1 == 0){

if(c1_m1 == 1){

c--;

c1_m1 = 0;

}

// When I add mores of this if´s, I start to have the problem with my PORTB outputs...

} // end checkmodules()

 

void module_status(){

if(c>0 && c<=3){

PORTBbits.RB4 = 1;

}

if(c==0){

PORTBbits.RB4 = 0;

}

if(c>=3){

PORTBbits.RB5 = 1;

}

if(c<3){

PORTBbits.RB5 = 0;

}

}// end module_status()

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2 answers to this question

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Hi!

I'm not sure that's happening, maybe we can find this together. First, check out this thread about PORT and LAT:

If you like to set an output, use LAT registers instead of PORT.

Second thing is your code: Is it your intention that variable c is going negative?

if (PORTAbits.RA1 == 0) {
    if (c1_m1 == 1) {
        c--;
        c1_m1 = 0;
    }
}

You used an "int" type, which means c is a signed 16 bit integer. You could use more explicit types like "int16_t" and check if your code regards the negative case properly.

Third thing I noticed: Your while() loop is running with maximum speed. It may be better to have a timing in your main sequence to get a more predictable runtime. For example, just add Timer0 to your main loop:

// configure TMR0 according to datasheet, section 20.2
OPTION_REG = 0b11010011;
while(1) {
    // wait here for next cycle
    while(INTCONbits.TMR0IF == 0);
    INTCONbits.TMR0IF = 0;
    
    // execute cyclic code
    // ...
}

About your floating output: How did you measure this? If you have used a multimeter, you likely are measuring the RMS value of a rapidly changing digital output. The TMR0 helps you getting a deterministic behavior, a scope helps you seeing what is really going on...

And did you halt the code at certain points and observed the behavior of your pins? With a PICKit or any other debugger attached to your controller, just run a debug session and set a breakpoint where you expect bad things to happen 🙂

 

 

 

 

 

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I would also suggest you take a look at this because you seem to be writing to the port register bits which will cause read/modify/write errors. Is it possible that the pin is actually toggling really fast? 

 

 

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