>-----Original Message-----
>From: piclist-bounces@mit.edu [mailto:piclist-bounces@mit.edu] 
>Sent: 07 October 2005 11:42
>To: Microcontroller discussion list - Public.
>Subject: RE: [PIC] Power Concerns - Can't get the chip to 
>start on my own voltage source
>
>
>In case anyone's curious, I solved the problem.
>
>I did the following two things:
>
>First, I added a ton of filtering caps: 220uF, 100uF, 10uF, 
>4.7uF, and 0.1uF.  That helped a good bit.  That let me use 
>the non-filtered voltage source and it would boot up 1/3 of 
>the time or so.
>
>That was still crappy, so I found the circuit diagram for the 
>olimex board and looked to see what it had that I was missing. 
> I noticed it had a resistor from the MCLR pin to the Vdd pin 
>through a 10k resistor. I looked up in the manual, and that's 
>how you enable POR.  Silly me... So, tossed the MCLR pin 
>through an 8.5k resistor (what I had on hand) to Vdd...  Boots 
>up every time.

Something sounds screwy to be honest.  A 10k resistor from MCLR to Vdd should be perfectly adequate (that's what most of my designs have).  The resistor does not "enable" power on reset as such.  What it does do is allow in circuit programming, and if combined with a capacitor and another resistor gives a delayed power on reset which can be helpful in some circumstances.  If the 10k was open circuit etc. then this would cause you a lot of problems.

I would check that you have the brown-out reset, and power up timer enabled in your configuration fuses, and that you have the correct oscillator configuration if you are using an external crystal/resonator. These are very important for reliable start up.

Regards

Mike

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