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

From: Clemens Koller
Subject: Re: [avr-chat] Endless loop in AVR?
Date: Sat, 28 Jul 2007 15:43:06 +0200
User-agent: Thunderbird (Windows/20070716)

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 
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 
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.

Clemens Koller
R&D Imaging Devices
Anagramm GmbH
Rupert-Mayer-Str. 45/1
81379 Muenchen

Phone: +49-89-741518-50
Fax: +49-89-741518-19

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