I often read that it is good practice to connect VCC with AVCC. Even in the ATMega8 datasheet it says so: AVCC is the supply voltage pin for the A/D Converter, Port C (3.0), and ADC (7.6). It should be externally connected to VCC, even if the ADC is not used. If the ADC is used, it should be connected to VCC through a low-pass filter. Note that Port C (5.4) use digital supply voltage, VCC. But nowhere I can find an explanation as to why they have to be connected. A simple circuit for blinking a LED works without connecting VCC and AVCC.

Do I just have to accept it, or is there a good reason? Mainly, it has to be connected because the manufacturer says it should. Aside from that, they should for full operation of the chip (all ports/pins), to prevent floating pin issues on the AVCC side, to prevent noise on the digital side.

There are issues where leaving the AVCC side unpowered causes parasitic power draw and can destablize the internal clock, or can prevent stable startup. Atmel designers have decided that having a separate Analog VCC and Ground is the best way of allowing relatively noise free analog section, by allowing users to add filtering and separation of the Digital and Analog Planes, even inside the ATmega. It's not just the ATMega8, afaik all ATMegas and even some ATTinys have this design. Good on you for asking for the reason! AVCC is specified as an independent pin because it connects to key analog components internally, and as such should have separate filtering capacitors.

This disambiguation page lists articles associated with the title Category. If an internal link led you here, you may wish to change the link to point directly to the intended article. The Saffir-Simpson Hurricane Wind Scale is a 1 to 5 rating based on a hurricane's sustained wind speed. This scale estimates potential property damage. Hurricanes reaching Category 3 and higher are considered major hurricanes because of their potential for significant loss of life and damage. The second point in this category is own cousin to the above. They belong entirely to the category of what is wise to realize good. D--n the rogues; I thought at one time they had me in a category! Categorical. Also called Guggenheim. (used with a singular verb) a game in which a key word and a list of categories, as dogs, automobiles, or rivers, are selected, and in which each player writes down a word in each category that begins with each of the letters of the key word, the player writing down the most words within a time limit being declared the winner.

Aug 9, 2011 - 'Absolute Maximum Ratings' are in all reputable data sheets and mean just what they say. They are the absolute maximum at which the device. Software update (ATMEGA) - directly from 'Device Programmer Desktop'. XPROG-M Hardware Specifications. 1pc x CD Software and User Manual.

Simple 'blinkenlights' projects don't have noise and accuracy requirements. Now if you mean if they should be connected to the same VOLTAGE, the answer is yes within +/- 0.3V of VCC From the: 'The ADC has a separate analog supply voltage pin, AVCC. AVCC must not differ more than ±0.3V from VCC.' And 'AVCC is the supply voltage pin for the A/D Converter' To recap: AVCC and VCC should be at the same voltage (within +/- 0.3 Volts), and it is identified as a separate pin to allow the designer to place extra filters on that input to keep noise out of the sensitive A/D converter portion of the IC. Hope that helps!

Often times, digital supply and ground pins will end up with small amounts of noise on them. It's hard to eliminate all such noise when digital circuitry is switching significant amounts of current, and 150mV or so of power-supply noise is unlikely to affect the circuitry powered by the digital supply pins. Having 150mV of noise on the analog supply pins, however, would make it very difficult or impossible for the analog circuitry to achieve fraction-of-a-percent accuracy. The fact that the analog pins are separated means that one can take accurate readings even if there is 150mV of noise on the digital power supply, provided that the digital supply doesn't swing by more than 300mV and one has an analog supply which is somewhere within 300mV of both extremes of the digital supply's range. Eliminating 99% of the noise from a power source that's only feeding the analog-supply pin, and ensuring that source voltage is close to the digital supply voltage, is often much easier than trying to eliminate all noise from the digital supply.