ATMega8 Schematic Circuit (Minimum system) is a support circuit for the microcontroller.
Without this support circuit, the microcontroller will not be able to work.
Minimum system for microcontrollers consist of several components. The components are : crystal, capacitors, and the reset circuit (consisting of resistors and capacitors).
And the crystal must be combined by two capacitors. The capacity of this capacitor should be in accordance with the AVR ATMega8 datasheet.
RESET pin on AVR ATMega8 must be pull up with a 4K7 ohm resistor and stabilized with ‘100nF capacitors’.
You have to make the pin as a downloader port. pin of the downloader port must meet a standard sequence. The pin sequence is: MOSI, MISO, SCK, RESET, GROUND.