> -----Original Message-----
> From: Fredrik Axtelius [SMTP:fredrik.axtelius@TELIA.COM]
> Sent: Tuesday, August 06, 2002 12:00 AM
> To:   PICLIST@MITVMA.MIT.EDU
> Subject:      [PIC][EE]: Unstable circuit
>
> Hi!!
>
> I have a PIC16F877 circuit and im having big problems to get it stable.
>
> Problem:
> It will only run for a short time and only if im touching GND with one
> hand.
> When I touch GND with one hand all I have to do is wave the other hand a
> few inces from the circuit to get it to reset, now if I keep that hand
> really still I can watch it run for like 5-10 secs before it lock ups (not
> resets).
>
> Hardware:
> All I have is a 4Mhz 16f877, osc caps are 27p
> One LED on RC4 with a resistor to GND.
> Max232 with all the caps on RC6 and 7. The other end of the max232 is
> connected to my com1.
> A reset button with a 10k pullup resistor.
> All my cables are short and nicely layedout and my powersupply delivers a
> stable +5v.
>
> What I have tried so far:
> I have tried to put +5 on either and both of the VDD pins, same thing with
> the VSS.
> I have put caps between none, either or both of the VSS/VDD pins.
> I disconnected the Max232 on rc6 and rc7, still the same problem.
> I tried a 16f874 at both 20 and 4Mhz, same thing.
>
> Help me!
> /Fredrik
>
You need to make sure that MCLR is tied to Vdd with a (e.g. 10k) resistor,
and also make sure that RB3 (PGM) is pulled low via another resistor if you
have low voltage programming enabled.

Regards

Mike

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