On 24/11/2010 22:45, David Duffy (AVD) wrote:
> The oscillator is a 20MHz 3 pin resonator and I have HS mode selected.
> Interestingly, the status (heat beat) LED flashes at the same rate in
> both good and fault conditions.
>
> The PIC has a 10K resistor from MCLR to Vdd, but no capacitor to Vss. If
> a reset it by shorting to Vss, the unit works fine again. It's only when
> the board is first powered up that the fault occurs.
>
> It's almost as though the UART is not initialising correctly. I have
> PWRTE enabled and the watchdog disabled.
>
> We replaced the PIC in the first faulty unit and it is behaving
> correctly now. I have done nothing to the second faulty unit and can
> replicate the fault easily.
>
> I'm loath to replace the PIC on the second board just yet, as I'd like
> to know why this is happening first.  Any ideas?  About the only thing I
> can think of is Vdd rising too slowly?
> David...
>
A resonator is inadequate for a UART. Some are barely better than=20
precision R C. You should be using a crystal.

--=20
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