ATTINY85 Pinout
ATtiny85 MCU · 8-pin AVR microcontroller with 5 usable IO; fun within the Arduino ecosystem.
| Pin | Name | Type | Function |
|---|---|---|---|
| 1 | PB5 · RESET/ADC0 | I/O | Reset / GPIO (reset by default) |
| 2 | PB3 · ADC3/XTAL1 | I/O | GPIO / clock input |
| 3 | PB4 · ADC2/XTAL2 | I/O | GPIO / clock output |
| 4 | GND | GND | Ground |
| 5 | PB0 · MOSI/SDA/PWM | I/O | GPIO / MOSI / I²C SDA |
| 6 | PB1 · MISO/PWM | I/O | GPIO / MISO / PWM |
| 7 | PB2 · SCK/SCL/ADC1 | I/O | GPIO / SCK / I²C SCL |
| 8 | VCC | Power | Supply + (2.7–5.5V) |
How to read the ATTINY85 pinout
- 01
Find pin 1
One end of the chip has a half-circle notch or a dot; with the notch facing up, the top-left pin is pin 1.
- 02
Count counter-clockwise
Count counter-clockwise from pin 1: go down the left side first, then up the right side from the bottom.
- 03
Check the table below
Look up each pin's function by number in the table below; power/ground are color-coded, and alternate-function signals are in parentheses.
Frequently asked questions
How many usable IO does the ATtiny85 have?
5 (PB0–PB4). PB5 is the reset pin by default; you can fuse it to act as IO but you lose ISP programming.
How do I flash it?
Commonly use Arduino as ISP over SPI (PB0 MOSI / PB1 MISO / PB2 SCK / PB5 RESET) to burn the bootloader or upload directly.
Can I use I²C?
Yes, you can implement I²C in software via the USI: SDA = PB0, SCL = PB2.
Pinout data comes from Microchip ATtiny85 datasheet (standard DIP-8 numbering). Refer to the actual device datasheet as authoritative for the pinout.