16F877A stopped when I touch its top

[Alex_rcpilot]

Hi all,this's weird.I soldered a board to run PIC16F877A with a crystal of 12MHz.An RC reset circuit and a connector to ICD2 is implimented.That's all.I don't understand why such a simple system can be so easily interfered when I touch the chip's top with my index finger.There must have been something I have neglected.Could anyone offer me a clue?Thank you!

 

[Jay.slovak]

I think you are missing capacitors, either 100nF at 5V to GND, or oscilators ~22pF. Also make sure that your MCLR or PGM pins are NOT floating...

 

[Mike - K8LH]

This symptom can also be experienced when;

(1) LVP is enabled in the configuration fuses and no pull-down resistor on the PGM pin...

(2) No pull-up resistor to VDD on the MCLR pin...

Good luck with your project...

Regards, Mike

 

[Alex_rcpilot]

I think you are missing capacitors, either 100nF at 5V to GND, or oscilators ~22pF. Also make sure that your MCLR or PGM pins are NOT floating...

This symptom can also be experienced when;

(1) LVP is enabled in the configuration fuses and no pull-down resistor on the PGM pin...

(2) No pull-up resistor to VDD on the MCLR pin...

Good luck with your project...

Regards, Mike

Hi Jay,I guess it's the latter case.
Yep,Mike,you're right.
As I went offline and retried to provoke the problem,I noticed it happened especially when my finger was close to the PGM pin.I searched through the datasheet and found all the answers on page 160.That's exactly what you guys are talking about here.The LVP was enabled in my circuit and RB3 was set as output,that's why the system went crazy with my touch.Thank you for your help.

Regards,Alex