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I am using ATmega8A standalone but analog pins (Port C) have not been use.

Due to ATmega8A does not have a PRR (Power Reduction Register) to disable ADC and TWI.

I would like to know, is it a work around solution to reduce the power consumption if AVcc is not connected?

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    You can disable the ADC on the ATMega8 the normal way. Though not the extra way that the PRR does. But I've found that the PRR doesn't do a whole lot. Disabling ADC, timers, and BOD and making the MCU sleep as much as possible is like 99%. – Gerben Jul 8 at 18:09
  • Unless the MCU allows you to apply power selectively (not the case of ATmega), failure to power some of the pins will result in some voltages applied in reverse internally, resulting in internal shorts. – Dmitry Grigoryev Jul 9 at 9:01
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No, the datasheet says power must be connected to Avcc. This is from the '328P, Atmega8A is similar but with less memory: (Microchip is taking forever to open the Atmega8A datasheet for me).

5.2.7 AVCC AVCC is the supply voltage pin for the A/D Converter (ADC), PC[3:0], and PE[3:2]. 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.

https://www.microchip.com/wwwproducts/en/ATmega8A

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No. You must connect AVcc even if you're not using the ADC. According to the datasheet:

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.

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