Power-on reset. Start-up timer.

[Lasse1]

Yes. I did.
And to be clear I can say that I am complete sure that my problem depend on power-up. (If I set the PIC in the holder with the pwr-leg bended away, and then connect it after the unit is powered-up, the pic starts correct)
You don´t have any other idea?
Friendly regards / Lasse

[mackrackit]

I am not sure what you mean by pwr-leg?
Can you post how everything is connected using pin numbers in the description or a schematic?

[Lasse1]

Hello.
Sorry about my defenition. I mean the VCC-pin. And I dont think that it is relevant how other pins are connected. I tried different connections and have the same troubble. The thing is that it is one sekund interrupts in the power supply every five sekund, and cause of that it is a condensator connected to the power supply to keep the pic alive. That is working fine, the troubble occurs only when it is powered up, and only when the condensator is connected. This was working fine with a basic stamp but a pic is obviusly more critical.

[BrianT]

Slowly rising power supplies will trip a PIC up. There is a minimum dV/dT of something like 5 V/uSec needed. RTFM will find it. No amount of resets will recover a PIC that has been powered up slowly.

I had this problem with a current limited power supply that slowly rose in voltage as it had to charge a big cap.

Minimise input storage capacitors, or put them direct across your PSU before the power switch so they can supply a burst current to the PIC circuitry and get the Vdd up within the allowed time.

HTH
BrianT

[Dave]

Lasse1 , You could also use an Processor supervisor device like MAX690 or something like it. It will hold the processor in reset until the power is stable and above the minimum level. The other thing it can do for you is an external watch dog timer as well as low power supply monitor...

Dave Purola,
N8NTA

[BrianT]

PIC18F4620 parameter D004 says 0.05V/mSec is the minimum dV/dT to get a reliable startup. A few years ago I had a dodgy system (with a Motorola xxxx supervisor chip) that was intermittent until I reduced the inlet filter capacitors to ensure faster voltage rise at power up.

Your mileage may vary but adding the supervisor did nothing for me.

HTH
BrianT

[Dave]

Brian, Actually, that is exactly what they are made for. I have used them for about the last 5 or so years on all of my products and projects. I have never had a problem with the reset line except when I forget to toggle the watchdog input.....

Dave Purola,
N8NTA