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'strange behaviour'
1999\04\07@111747 by Sebastián Dols

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Ok, I have detected a strange behaviour in my 16f84 last nigth, and I want
to share with you.

Imagine a 16f84, ceramic resonator 1Mhz, _MCLR to Vdd, five leds in rba0:4,
with no current limiter resistor in the led paths. portb is all input,
interrupt in rb4:7 change (nothing strange, I think). Program coded to shift
led blinking, period 1 sec, change of direction on portb signal. No problem
to compile, no problem to run, all OK... But if NO 5V to  the PIC vdd pin,
if 5V (signal) is applied to any of portb pins, all the leds in porta are
emitting light at the same time...

Someone knows what happens? I suspect about my protoboard, but there is no
way between 5V to the leds to GND if i remove the PIC (the leds do not emit
in that case, of course)


Thanks in advance, keep on PICing.

1999\04\07@112430 by Justin Crooks

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Obviously, there is a path to Vdd through the PIC.  You're probably
damaging the PIC, as you are passing current through it in an
unconventional manner.  I recommend keeping Vdd on, any time there is power
to the board :)


----------
> From: Sebastian Dols <spam_OUTsdolsTakeThisOuTspamESEGI.ES>
> To: .....PICLISTKILLspamspam@spam@MITVMA.MIT.EDU
> Subject: strange behaviour
> Date: Wednesday, April 07, 1999 9:17 AM
>
> Ok, I have detected a strange behaviour in my 16f84 last nigth, and I
want
> to share with you.
>
> Imagine a 16f84, ceramic resonator 1Mhz, _MCLR to Vdd, five leds in
rba0:4,
> with no current limiter resistor in the led paths. portb is all input,
> interrupt in rb4:7 change (nothing strange, I think). Program coded to
shift
> led blinking, period 1 sec, change of direction on portb signal. No
problem
> to compile, no problem to run, all OK... But if NO 5V to  the PIC vdd
pin,
> if 5V (signal) is applied to any of portb pins, all the leds in porta are
> emitting light at the same time...
>
> Someone knows what happens? I suspect about my protoboard, but there is
no
> way between 5V to the leds to GND if i remove the PIC (the leds do not
emit
> in that case, of course)
>
>
> Thanks in advance, keep on PICing.

1999\04\07@112838 by Kevin Fisk

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face
Let me get this straight; the PIC has no 5V power, but you have 5V power
to the LED's ?

If that's the case, then your LED's are probably turning on through the
protection diodes, which is effectively a diode between the port pin and
Vcc.

Sebastian Dols wrote:
{Quote hidden}

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