test pic16f877 with led

[alaalwi11]

hi anyone here, it first time to program microcontroller practical
i begin with pic16f877 with simple program to light and turn off led with delay
at begining the circut work correctly but after few test it damaged
i try to connect it again but there are no result
can any one give me some suggestion

 

[hexreader]

You should put a resistor in series with the LED. Something like 330 Ohms maybe.

Either disable Low Voltage Programming in your configuration bits, or connect a 1k resistor from pin 36 (RB3/PGM) to ground.

The rest of the schematic seems reasonable, assuming that you are supplying good, stable power.

 

[bigdogguru]

You need a current limiting resistor inline with the LED. Otherwise the you'll exceed the 25mA max source/sink per I/O pin current rating.

What was damaged the LED or PIC?

 

[dayanpad]

If it worked at the binging, current problem is man made problem
very difficult to solve such a problem, because real scenario with you

you have to follow following steps

first check MUC working order (using programmer) ( hardware ok , MCU found)
second check your hardware ( MCLR pin voltage 5V)
if you use 7805 IC try to change with new one
double check your power supply ( apply nose less power)

 

[alaalwi11]

hello friends ,thank for reply
firstly in practcal experiment i use 150 ohm resistor with the led
secondly i use 7805 regulator circuit and it supplied 5v accuracy

thirdly as i say the circuit worked correctly at first and then it sometime works with error or doesn't work
finally there is some abnormal behavior when i connect the circuit completely the led dosn't work and when i disconnect the ground
from vss the led light continuously

Best regards,

alaalwi11

 

[hexreader]

So what about LVP? Have you disabled it in code or from your programming software?

Have you tried 1k resistor from PGM pin to ground?

(see post number 2)

 

[KerimF]

Try to reset the PIC manually; a momentary short to ground on pin 1 (MCLR).

 

[alaalwi11]

thank you indeed
my code is following :



void main()
{
TRISB=0;
loop:
PORTB=0xff;
delay_ms(1000);
PORTB=0;
delay_ms(1000);
goto loop;
}

i use the following digram after exchange pic16f84a by pic16f877 and change to adequate connection
using datasheet