Connecting avref and avcc in atmega8

[manshuk89]

i am currently using an atmega8 to control my lcd.
i am using ic7805 voltage regulator to provide for its vcc.

i have shorted avcc to vcc. should i do the same for avcc as well... or does it need some other external reference?

 

[MATLABdude]

i am currently using an atmega8 to control my lcd.
i am using ic7805 voltage regulator to provide for its vcc.

i have shorted avcc to vcc. should i do the same for avcc as well... or does it need some other external reference?

AVcc is the power supply for the Analog to Digital Converter (ADC), and AVref can be used for decoupling of the internal reference (i.e. it doesn't need to be connected to anything, unless you want to use a capacitor here to increase noise immunity while using the ADC). From the Atmega8 datasheet:

The ADC converts an analog input voltage to a 10-bit digital value through successive approximation. The minimum value represents GND and the maximum value represents the voltage on the AREF pin minus 1 LSB. Optionally, AVCC or an internal 2.56V reference voltage may be connected to the AREF pin by writing to the REFSn bits in the ADMUX Register. The internal voltage reference may thus be decoupled by an external capacitor at the AREF pin to improve noise immunity.

http://www.atmel.com/dyn/resources/prod_documents/doc2486.pdf

 

[Xitami]

in ATmea8 avcc and vcc are shorted internaly, mega88 works better
7805 as reference?

 

[MATLABdude]

in ATmea8 avcc and vcc are shorted internaly, mega88 works better
7805 as reference?

AVcc and Vcc are *not* shorted internally, according to the (short) pin description, and AVcc should be connected to a supply (Vcc or otherwise) even if the ADC is not being used (page 6):
http://www.atmel.com/dyn/resources/prod_documents/2486S.pdf

The 7805 is being used to supply Vcc, stepping it down from whatever >5V supply is being supplied.

 

[Xitami]

http://www.avrfreaks.net/index.php?name=PNphpBB2&file=printview&t=20967&start=0"

 

[MATLABdude]

http://www.avrfreaks.net/index.php?name=PNphpBB2&file=printview&t=20967&start=0"

Well, that's a rather major oversight! Unfortunately, given that it's now 'legacy', I imagine that it may also be in the Atmega8A, as well (though, oddly enough, it has the same description in the pin description, which suggests that it's been decoupled):
http://www.atmel.com/dyn/products/product_card_v2.asp?PN=ATmega8A