Re: [avr-chat] Endless loop in AVR?

[Clemens Koller]

Wojtek Dabrowski schrieb:
> > > One problem though - I seem to be doing something wrong with the reset.
> > > When I press the reset button, I connect the reset pin to Vcc (+5V).
> > RESET on AVR's are active low.  Use a 10k Pull-Up resistor from
> > the RESET pin to Vcc, and connect your button from the pin/resistor
> > to ground.
>
> Thanks, I'll do that!
>
> > You must have a background with 8051's where RESET is
> > active high?
>
> Actually, no, I haven't touched microcontrollers before. I'm just used
> to +5V meaning that there is a signal, and ground meaning there is no
> signal (from technical informatics courses, where you build simple stuff
> from NANDs and NORs), so I kind of assumed that the reset would be
> active high.
>
> Thanks for the help, I'll try those things now - I hope this depleted my
> repertiore of noob-questions for now :)

Usually, active low signals are marked with as /RESET or RESET# or INT_ or 
similar.
The / or # should tell you that this signal is asserted (active) when it's low.
Low usually means connected to GND and high usually VCC (GND=0V, VCC=1.8V, 
3.3V, 5V, ...)
There are even some datasheets where you have i.e. an active low pin marked
with "RESET". The "inversion" is then done with a small "o" circle on the pin 
symbol.
IMHO not an error prone version.

Then, take care about the initial values on power up and when the uCtrl
is asleep (and the ports are "floating or weak or tbd.").
It doesn't make sense to take a uAmps uCtrl when it's asleep if one
of your port pins still needs to drive some mAmps.

MOSFETs and Buffers are great to split away the low power uCtrl from
the current drawing circuits.

Regards,
--
Clemens Koller
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