Communication with an ATtiny and Arduino. For saving Pins.

Using Arduino Microcontrollers
4

wher's the USI on the ATTINY?

Have a look at the data sheet.

MOSI pin5
MISO pin6
SCK pin7

But you don't need MISO because you are only talking one way.

is it two wires?

Yep, see above.

where to I connect it to on the Arduino?

Any two pins you like if using shiftOut(), or the SPI pins (SCK and MOSI) if you want to use the SPI hardware.

but one thing

Actually that's three things :slight_smile:

Rob