Is crystal mandatory on attiny84? I am trying to make a mini project with attiny84 and I searched the web so I can make an arduino on breadboard. What I saw on the internet is that they didnt use crystal. Is it mandatory if I want to use 1 pwm pin and the SPI interface on the attiny84?
Only if you need crystal accuracy. If the internal RC oscillator is accurate enough then feel free to use it instead.