ATTINY84 - Accessing PB3 (hardware pin 4)

Using Arduino Microcontrollers
1

I'm working on my first project using a non-standard microcontroller so this might seem like a beginner's question. The standard Arduino core for the ATTINY84 assigns pin numbers 0-10 to 11 of the microcontroller's pins, but I need to access all 12. How do I address that 12th pin? Its hardware pin 4, port pin PB3, functional name PCINT9/XTAL2.

The diagram as given in the header file is:

//                           +-\/-+
//                     VCC  1|    |14  GND
//             (D 10)  PB0  2|    |13  AREF (D  0)
//             (D  9)  PB1  3|    |12  PA1  (D  1) 
//  (Need this one)    PB3  4|    |11  PA2  (D  2) 
//  PWM  INT0  (D  8)  PB2  5|    |10  PA3  (D  3) 
//  PWM        (D  7)  PA7  6|    |9   PA4  (D  4) 
//  PWM        (D  6)  PA6  7|    |8   PA5  (D  5)        PWM
//                           +----+
2

Never mind...my brain was confusing hardware pin 3 and port pin PB3. Problem solved!

3

If the core you're using doesn't support it, you can add the definitions for that pin easily enough (not sure which cores do and don't provide a mapping for it - I know some do; my 841 core cribbed that header from and 84 core that defined it ) - however because that's the reset pin, that pin is generally not useful; you need to blow reset disable fuse - since the reset pin in necessary for programming it, you typically need HVSP to unset that fuse so you can reprogram it again. Plus, reset pin is a crappy output, much weaker.

...
(as an aside - I just realized that if I used a bootloader with a longer delay than normal, and went back in time to when we didn't have the DTR reset trick and had to push reset to reprogram our boards, I could still reprogram it through the bootloader... just awkwardly.

4

KalebPSpector:
Never mind...my brain was confusing hardware pin 3 and port pin PB3. Problem solved!

So how did you solve the problem? What pin number should be used for PB3 (Reset pin) in a program?

5

11 should work - but you need to have set the RSTDSBL fuse (otherwise the pin only acts as the reset pin), which means you cannot program it using an ISP programmer (like the common USBAsp, Arduino as ISP, etc) - only using HVSP.

In HVSP, a different command set and different pins are used, and RST is held at +12v - this means different hardware is required (either you need to make or buy, and they're not $2-3 like USBAsps), and that your design must either allow you to disconnect other things from the reset pin before programming it, or not have anything on that pin that would be damaged by that +12v.