Why when I press my reset button it cannot reset again just the 1st time i pressed the led turn off and cannot on again.
i follow the schematic here to connect the reset button.
http://www.e-shore.com.my/homepage/schematics/basic-circuit/14-basic-circuit-for-pic16f877a.html

 

Are your programmer connected. It take control over the MCLR pin. Try to disconnect the programmer. And see if that help

 

Is it running from 5V? I use a 4.7K or 10K pullup resistor on MCLR, 1K is a bit strong.

 

Is it running from 5V? I use a 4.7K or 10K pullup resistor on MCLR, 1K is a bit strong.

ya.from 5v.but what do you mean 1k is a bit strong?not 10k stronger than 1k?

 

Are your programmer connected. It take control over the MCLR pin. Try to disconnect the programmer. And see if that help

my programmer is not connected.how?

 

nobody can help?oh no!

 

It would help if you posted your code (use the "Go Advanced" button and wrap your code in the code tags "#" so that it easier to read. Without the code its hard to say what is going wrong.

 

ya.from 5v.but what do you mean 1k is a bit strong?not 10k stronger than 1k?

An 10K resistor only needs 1/10 the current of an 1k resistor to pull the voltage down to a low voltage.

Note: No idea if that is the cause; I would guess I code issue; but, I am mainly a programer instead of a hardware person. So, I always look to eliminate what is easier for me to check. After checking the normal hardware things on PICs.

Normal hardware Items to check.

Note: I have seen PICs partly work without one of Power or Ground Pins connected.

Ground to PIC
Power to PIC
MCLR properly connected; the proper connection can vary some per configuration options.
If using external Crystal is it connected with the recommend capacitor(s)
Check the rest of the schematic connections.

Tim S.

 

I think there're 3 things to do:
1. change the pull-up res from 1k to 4.7k
2. add a 1uf cap between MCLR and GND
3. Make sure the load cap of the crystal is correct. Most load caps of crystal are from 10 to 20p. 30p may be a little bigger.

 

ya.from 5v.but what do you mean 1k is a bit strong?not 10k stronger than 1k?

Think of it this way: If you have a 1 ohm resistor tying a pin to 5V you will not be able to pull it away from that 5V. But if a 10K ohm resistor is used you can easily pull it away from the 5V. Therefore, 1 ohm is "stronger" than 10k ohm.

 

The circuit is ok,it will work properly but your switch might cause the problem so buy good quality switch.I did the same mistake when I was starting with these stuffs...

You can use this circuit for reset...

 

Is it running from 5V? I use a 4.7K or 10K pullup resistor on MCLR, 1K is a bit strong.

I connect my /mclr to 5 volts !

 

Thenever I can (working with PICs) I disable the MCLR function.

 

Is it on a breadboard? It can be common to get a problem where the PIC xtal oscillator does not re-start after MCLR reset. Usually caused by long wires and/or too much capacitance near the xtal caused by the breadboard.