problem in blinking led with 16f877a

[hassankhan]

i wrote a program in mikro c & put it into 16f877a, led didnt glow but when i touch one of the probe of multimeter with vdd pin of controller & other with osc2 then it was glowing, what is this?
please tell where i m making mistake??

code is

void main() {

TRISB = 0; // TO MAKE ALL PORT OUTPUT
     PORTB = 0; // TO OFF PORTB
     while(1)
     {
     PORTB = 0xff; // TO TOGGLE PORTB

     }
}

thanks & regards
hassan khan

 

[Ian Rogers]

Have you built this on bread board..

 

[dougy83]

Make sure you have a vcc decoupling capacitor next to the pic power pins. Also make sure you are using the correct oscillator configuration, whether it be crystal, rc or internal. These will require additional capacitors, a resistor and capacitor to operate correctly

Also note that your code to toggle the port pins is incorrect; try using PORTB ^= 0xFF;

 

[House0Fwax]

Maybe stick a delay in there, so you can see the difference between on and off.

 

[hassankhan]

Have you built this on bread board..

yes this on bread board,why sir?

 

[hassankhan]

Make sure you have a vcc decoupling capacitor next to the pic power pins. Also make sure you are using the correct oscillator configuration, whether it be crystal, rc or internal. These will require additional capacitors, a resistor and capacitor to operate correctly

Also note that your code to toggle the port pins is incorrect; try using PORTB ^= 0xFF;

i m not toggling the port just constantly glowing an led

 

[hassankhan]

sorry i made mistake in title i m not blinking an led , i wanted to glow led constantly

 

[Ian Rogers]

yes this on bread board,why sir?

Because the bread board already has capacitance... leave the crystal caps off and try it.. also make sure,as Dougy said, that there is a decoupling cap 0.1μ is across the pic power pins..

 

[hassankhan]

now i have placed 0.1 uf cap between vdd & vss but still led is not glowing & now when i m placing my one probe on vdd & other on osc2 it is not glowing as well as previously it was,what is it?

 

[dougy83]

Have you disabled the WDT? This is done through the configuration bits, or you can leave it enabled and just clear it in the main loop using whatever mikroC's equivalent of asm("clrwdt") is.

If it's still not working, to check if it's just your oscillator setup, you can try using the internal oscillator.

 

[hassankhan]

Have you disabled the WDT? This is done through the configuration bits, or you can leave it enabled and just clear it in the main loop using whatever mikroC's equivalent of asm("clrwdt") is.

If it's still not working, to check if it's just your oscillator setup, you can try using the internal oscillator.

i am unaware of programming of internal oscillator can u provide me hex file to glow led on portb?

 

[Ian Rogers]

Have you got the complete code for us to look at? Not just the first snippet...

 

[House0Fwax]

you can try using the internal oscillator.

That PIC doesn't have one.

 

[dougy83]

That PIC doesn't have one.

True.

 

[alec_t]

Do you have a current-limiting resistor in series with the LED? If not, the LED may be pulling a pin voltage too low.

 

[House0Fwax]

Another thought, do you have 'MCLR' (Pin 1) held high?

 

[hassankhan]

Do you have a current-limiting resistor in series with the LED? If not, the LED may be pulling a pin voltage too low.

it has

 

[hassankhan]

Another thought, do you have 'MCLR' (Pin 1) held high?

yeah i have

 

[hassankhan]

Have you got the complete code for us to look at? Not just the first snippet...

void main() {

TRISB = 0; // TO MAKE PORTb OUTPUT
PORTB = 0;
while(1)
{
PORTB = 0xff; // TO set portb

}
}

it is my code

 

[Ian Rogers]

Where's the rest of it.... This couldn't possibly have compiled... What compiler are you using...