I can get PB4 to work but not PB3 on my ATtinny85. I'm just lighting up an led (with 150 ohm resistor) (using internal 16mhz)

void setup() {
  pinMode(3, OUTPUT);
  pinMode(4, OUTPUT);

void loop() {
  analogWrite(3, 15);//does not work
  analogWrite(4, 15);//works
  analogWrite(3, 0);//does not work
  analogWrite(4, 0);//works

enter image description here

  • 1
    According to the diagram, only PB0 and PB1 support PWM (purple).
    – Gerben
    Dec 27, 2019 at 19:22

1 Answer 1


The hardware PWM is only suported on pins with output compare altenate function on it. The pinout in your question shows Attiny13 but the rest of your question is about Attiny85, which has different capabilities from Attiny13

Attiny85 pinout

As you can see, only pins with PWM capability are PB0, PB1 and PB4

  • ohhh, thank you, i didn't even realize i was looking at the 13a pinout by mistake Dec 28, 2019 at 15:29

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