MCLR problem with PIC 16f877a

[asharwahid]

Salam to everyone!
Can anybody help me in resolving the following problem...!

MCLR pin is connected with the following components:

C=100nF
R1=10k
R2=2.2k

:?:Sometime when i switch ON the circuit it turns ON, and sometimes it requires a manual reset by shorting the capacitor legs.
I require 100% guarantee to switch ON. and it never need any more manual reset.

Thanks

 

[debjit625]

A 10K pull up resistor will do it.Your mcu must have two Vdd and Vss pins they must be powered properly.If your power supply gives slow ramp up then you have to use a different type of external power on reset circuit...

Good Luck

 

[emresel]

Hi;
Increase R1 some more (may be 20K) or decrease R2 some (however it is written in spec it should be greater than 1K, i would prefer 100R or 470R)
Good luck

 

[papunblg]

In order to avoid any error which may occur on Brown-out reset, the PIC 16F887 has built in 'protection mechanism'. It is a simple, but effective circuit which responds every time the power supply voltage drops below 4V and keeps this level for more than 100 micro seconds. This circuit generates a reset signal and since that moment the whole microcontroller operates as if it has just been turned on.

So check Vcc. Also check c1 if its working ok.

Also you may try the following:-


.............also check __CONFIG entry