Digispark USB ATTiny85 Usage Tips

Usage tips and examples for the Digispark USB ATTiny85 clone. Built-in LED resides on the pin 1 (PB1)

This README also contains info about programming of the Digispark USB ATTiny85 clone with the Bus Pirate

Program Micronucleus bootloader to the ATtiny85

Tools versions

• avrdude - 6.3
• micronucleus bootloader - v2.5
• Bus Pirate device - v3b custom mod

Hardware connection

Bus Pirate	Digispark ATtiny85
GND (BR)	GND (or pin4)
+5V (OR)	5V (or pin8)
CS (WT)	P5 (RESET)
MOSI (GR)	P0 (MOSI)
MISO (Blk)	P1 (MISO)
CLK (PU)	P2 (SCLK/CLK)

Program commands cheat sheet

Check buspirate connection:

avrdude -P /dev/tty.usbserial -c buspirate -p t85 -v

Flash Micronucleus bootloader and set default Digispark fuses:

curl -LO https://github.com/micronucleus/micronucleus/raw/v2.5/firmware/releases/t85_default.hex

avrdude -P /dev/tty.usbserial -c buspirate -p t85 -b 115200 -U flash:w:t85_default.hex -U lfuse:w:0xe1:m -U hfuse:w:0xdd:m -U efuse:w:0xfe:m

Additional information

• The default fuses for a Digispark board:

  • ATtiny85 Lfuse: 0xE1 - (digispark default) PLL Clock + Startup 64 ms
  • ATtiny85 Hfuse: 0xDD - External Reset pin enabled (Pin5 not usable as I/O) + BOD 2.7 V + Enable Serial Program and Data Downloading
  • ATtiny85 Efuse: 0xFE - self programming enabled. BOD enabled requires additional 20 µA in sleep state and therefore may be not desirable for low power battery applications. To disable BOD, use 0xDF as Hfuse.

• AVR fuses calc: https://www.engbedded.com/fusecalc/

• Microcontroller pinout cheat sheet: https://tinkerlog.com/2009/06/18/microcontroller-cheat-sheet/

• Bus Pirate AVR Programming: http://dangerousprototypes.com/docs/Bus_Pirate_AVR_Programming

Serial console (UART)

Digispark ATTiny85

dtiny core TinyDebugSerial overrides Serial and uses:

• PB3 as TX for CPU frequencies <= 8MHz
• PB2 as TX for other frequencies

See TinyDebugSerial.h for the details

Generic ATtiny85

tiny core TinySoftwareSerial overrides Serial and uses:

• AIN0 (PB0) as TX
• AIN1 (PB1) as RX

See src/main.cpp for the example.