erratic start-up 16f876

[RonDumas]

Hi all.
I have a board with a pic and a
**broken link removed**controlling a few relays.
All seemed well until a power failure today.
When the power was restored the Siteplayer and webpages worked but the pic didn't fire-up.
I tried a new pic and the same result.
Half the time the pic starts and half the time it just sits there.
Pic is a 16f876
4mh crystal
2-22pf caps
10k resistor in series with MCLR
+5 volt on pin 20
0v on pin 19
wdt "off"
bor "on"
por "on"

Power from a 12vdc 100ma wallwart thru a 7805 regulator
actual voltage on pins 19 + 20 = 4.98 vdc


I'm stumped.
This board is new and I'm just testing it out so there's no past history of stable operation. Could be in the original design.
Thanks in advance for any help. :wink:[/url]

 

[RonDumas]

sorry for the double post

 

[RonDumas]

I found this.

I found this on Microchip's website. After reading it I lowered the caps to 15pf and changed config. to HS. So far very stable operation. I thought the 4mhz crystal and 22pf caps was the rule. I was wrong.


https://www.electro-tech-online.com/custompdfs/2004/08/osilator.pdf