Shift register on Attiny85 programmed by Arduino

Question

Shift registers need 3 digital pins in order to work (data, clock and latch), but Attiny45/85 chips provides 2 digital and 2 analog pins.

Would I use 1 analog pin as digital pin? How?

• Martynas: forum.arduino.cc/index.php?topic=170470.0 this can be helpful
• whitenoisedb: well that's an unanswered question i guess
• Martynas: Thats why its in comments i guess
• Ignacio Vazquez-Abrams: Claiming only 2 analog pins must mean that you're using attiny instead of arduino-tiny; I recommend that you use arduino-tiny instead.

Answer 1

The ATtinyX5 does not have any analog-only pins; all 5 pins are usable as digital I/O (all 6 if you know what you're doing, but if you need to ask how then you're not ready to do so).

• whitenoisedb: well, I mean if I had to declare them as OUTPUT using pinMode(). Should I use digitalWrite() and digitalRead() on them?
• Ignacio Vazquez-Abrams: That's how you use digital I/O with the Arduino libraries, so yes.

Answer 2

As Ingnacio has already pointed out, PB0 to PB4 can be used as digital IO ports without problems. It night be a good idea though not to touch PB6, the RESET pin.

Btw, this isn't different from an Arduino, where all so-called analog pins can be used for digital output as well.

If you want to drive shift registers from an ATtiny85 using SPI, you might want to have a look at the tinySPI library written by Jack Christensen. Please note that I haven't used this library personally!

• whitenoisedb: Thanks. I'll read about SPI. I know attinyX5 uses USI, but communication is possible with that library and SoftwareSerial I guess.