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Re: [avr-chat] Getting started with an ATmega48

From: Carl Petter Levy
Subject: Re: [avr-chat] Getting started with an ATmega48
Date: Fri, 01 Jun 2007 08:42:05 +0200
User-agent: Thunderbird (Windows/20070326)

Matthew MacClary skrev:

    1. What voltage should I connect to Vcc?  It seems to imply that
    it can
    work at 5V or 3.3V, but no actual limits are given.

The Atmega48 is available as both a 5V and 3.3V versions, as well as a 1.8V version I believe. Where did you get your chip, and what part number is printed on it? If the chip came as part of a hobby kit of some sort, then I might go out on a limb and suggest that it is a 5V part. However hooking 5V to a low voltage part will damage it, so be sure before you power up or you might be out $2.69 or so.

The ATmega48 is available as normal, and ATmega48V (low voltage edition). The ATmega48 will operate at any VCC between 2.7V and 5.5V for frequencies below 10MHz. If you run it at frequencies higher than 10MHz (up to max 20MHz) VCC must be between 4.5V and 5.5V. The low voltage version ATmega48V will operate at up to 4MHz for any voltage between 1.8V and 5.5V, if you want to run it at frequencies faster than 4MHz (max 10MHz), VCC must be between 2.7V and 5.5V. So the low voltage part will also run on 5V.

The default fuses will run the part on 1MHz. This means that if you have the normal edition any voltage from 2.7V to 5.5V will do, and for the low voltage edition any voltage between 1.8V and 5.5V is OK. Running (or attempting to) run a normal part at 1.8V will not damage the part, but we have no guarantee that the part will operate correctly. The same is true if running a part at too high frequencies and at too low voltage. Running above 5.5V may well damage the part.

Carl Petter

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