[SOLVED] help please Problem with PORTB when using TMR0 on pic16f877A

[shaolinyo]

hello, i used tmr0 for timing , i dont use portb , but when i run the simlation i get that portB is set with a value 1




and that is the code:

 int t=0;   //time counter

void interrupt()
{
  if(INTCON.T0IF){
          t++;      //for evry inettruption occure we increment t
          TMR0=150;//the value to start the tmr0 if is spesified in the main program
}

  INTCON.T0IF=0;

}
void main() {


Option_Reg=0b00010000;
INTCON=0b10100000;


trisc=0;
portc=0;


TMR0=150;
for(;;){

       if(t==1)
           portc.rc1=0;
       if(t==2) {
        portc.rc1=1;
        t=0;

       }


}

}

thank you

 

[betwixt]

You have Bit 7 (-RBPU) of OPTION_REG programmed to zero, that turns on the internal pull-up sources to PORTB and will make any pin not actively driven low appear to have a high logic level on it.

Try changing OPTION_REG to 0b10010000 and see if it fixes the problem.

Brian.

 

[KlausST]

Hi,

"Pullup" is not that bad.

General rule: Don't let (unused) pins floating. This is true for any circuit, digital as well as analog.

Klaus

 

[shaolinyo]

KlausST thank you for the advice , but what you mean by pins floating , and what is its impact on the circuit?

 

[KlausST]

Hi,

but what you mean by pins floating

"floating" is a quite commom phrase.
"floating" = "high impedance" = not driven by anything. No internal drive, no external drive (like pullup, or pulldown).

and what is its impact on the circuit?

This has been discussed many times before:
* Increased supply current
* oscillations
* no valid state
* increased EMI
* EMC problems
*...

Klaus