The ATTINY85-20SU is an 8-bit AVR microcontroller from Microchip in SOIC-8, running at 20MHz with 8KB Flash, 512 bytes SRAM, and 512 bytes EEPROM. Despite having only 6 GPIO pins (8-pin package, 2 pins for power), the ATTINY85 packs an impressive peripheral set through pin multiplexing. The 10-bit ADC has 4 channels with 15ksps, usable for analog sensor reading. Two 8-bit timers (Timer0 and Timer1) provide 4 channels of PWM, useful for LED dimming and motor speed control. The USI (Universal Serial Interface) can be configured as SPI master/slave or I2C master/slave, providing communication flexibility. The analog comparator with configurable reference is useful for zero-crossing detection and threshold monitoring. The ATTINY85 supports ISP (In-System Programming) via SPI (MOSI/MISO/SCK on PB0-PB2) and debugWIRE (single-wire debug on RESET/PB5). The 8KB Flash supports 10,000 write/erase cycles. The -20SU suffix specifies 20MHz, SOIC-8, industrial temperature (-40C to +85C). The ATTINY85 is the go-to MCU for minimal-footprint projects: Digispark USB development board, LED controllers, keyboard controllers, and I2C sensor nodes. The internal RC oscillator runs at 8MHz (calibrated to +/-10%), with a 6x PLL option for 48MHz USB-compatible clock. Active current is 3mA at 5V/20MHz, and power-down current is 0.1uA.