Re: help - weird intermittent resets

As my old teacher in electronics always said...

Have you measured the circuit?

No, not with a DVM!  With an oscilloscope!

You cannot claim a rock solid 4.85V from the supply until you measured
it with an oscilloscope. 

Cheers

Dan


On Sat, 2005-07-30 at 14:13 +1200, David McNab wrote:
> Hi,
> 
> I'm getting a weird and frustrating problem with a pic18f252 that
> intermittently resets itself.
> 
> I've reduced my test program to the bare essentials - pseudo-code is:
> 
>  - clear trisc.0
>  - while true
>      - reset portc.0  # turn on piezo buzzer
>      - wait 1ms       # long enough to click buzzer
>      - set portc.0    # turn off buzzer
>      - wait 249ms
> 
> Config:
>  - wdt and bor are on
>  - 20 MHz crystal, with 18pF caps to ground
> 
> Observations:
>  - pic resets at random times, varying between 1s and 20s
>  - pic resets much less often when I disconnect the
>    max232-based tty interface
>  - pic resets less often with much smaller progs (eg, the above
>    test prog written in c and compiled under ccs, as opposed to written
>    in forth and bloated out to 4k by the vm and support code)
>  - power supply is delivering rock-solid 4.85 volts
>  - i cannot reproduce this resetting when running the prog via gpsim
> 
> Thoughts:
>  - crystal is dodgy, locking up
>  - pic is affected by ambient electrical noise
> 
> Any ideas on cause, and fix/workaround?
>