Blinking an LED using an ATTiny85 programmed with avr-gcc and avrdude on Mac OS X.

Using Homebrew, tap larsimmisch's homebrew-avr repository:

brew tap larsimmisch/avr
brew install avr-libc

1. Compile with avr-gcc
2. Prepare the hex file with avr-objcopy
3. Flash the hex with avrdude

avr-gcc -Wall -Os -DF_CPU=1000000 -mmcu=attiny85 -o hello.o hello.c
avr-objcopy -j .text -j .data -O ihex hello.o hello.hex
avrdude -c usbtiny -p t85 -U flash:w:hello.hex:i

F_CPU must be defined at the avr-gcc command line or above the #include <util/delay.h> so the delay library knows the microcontroller's clock speed.

Wire the ISP-6 cable from the USBTinyISP to the breadboarded ATTiny85 using jumpers.

Looking at the ISP-6 cable with the connector key at the bottom, the pins are numbered like this:

+-----------+
|(6) (4) (2)|
|(5) (3) (1)|
+-----------+
     |_|

1. MISO
2. Vcc
3. SCK
4. MOSI
5. Reset
6. Ground

(See also this photo)

The ATTiny85's pins are:

 (8) (7) (6) (5)
+---------------+
|               |
| o             |
+---------------+
 (1) (2) (3) (4)

1. PB5 (Reset)
2. PB3
3. PB4
4. Ground
5. PB0 (MOSI)
6. PB1 (MISO)
7. PB2 (SCK)
8. Vcc

Connect the ISP and the ATTiny85 together on the Ground, MISO (Master In, Slave Out), MOSI (Master Out, Slave In), SCK (Serial ClocK), Reset, and Vcc pins:

• ISP-6 pin 1–ATTiny85 pin 6 (MISO)
• ISP-6 pin 2–ATTiny85 pin 8 (Vcc)
• ISP-6 pin 3–ATTiny85 pin 7 (SCK)
• ISP-6 pin 4–ATTiny85 pin 5 (MOSI)
• ISP-6 pin 5–ATTiny85 pin 1 (Reset)
• ISP-6 pin 6–ATTiny85 pin 4 (Ground)

N.B. The ATTiny's pins 2 and 3 are unconnected.

Power the LED with a transistor and a series resistor, switching the transistor using a resistor from the ATTiny's pin 2 to the transistor's base.

• Honey, I Shrunk the Arduino
• ATTiny85 and ISP-6 pinouts
• ATTiny85 pinout
• Atmel's in-system programming documentation