First, I'm kinda new to this AVR world, please don't be too hard.

I'm running into a very simply problem. I'm trying to use the ATTiny85 inside the Arduino framework, but without the Arduino functions digitalRead or digitalWrite (too slow). I have no problem writing signal to pins (PORTB &= 0b00000001), But whatever I try, I'm not able to READ from the pin (PINB & 0b0000001).

However, this is not entirely true. whatever I try (PINB & 0b000001, PINB & 0b000010, PINB & 0b000100, I'm always value reading from the PIN 0 (physical pin 5). Does anyone have try to read the ATTiny pin without the Arduino function ? I'm simply trying to do digital read here. (no analog) Here a sample code which reproduce the problem.

  DDRB = 0b00001000; // set the LED pin as output.
  while (1) 

    if ( PINB & 0b00000010 != 0) // read the PIN to check if the button is pressed.
      PORTB = 0b00000000; //Turn Off the LED when the button is pressed
      PORTB = 0b00001000;  //Turn on one LED by default
  • 3
    \$\begingroup\$ Operator precedence. != comes before &. Brackets are your friend. \$\endgroup\$ – Tom Carpenter Apr 11 '16 at 19:49
  • \$\begingroup\$ Damn, you are right.... If this is my only problem, I good for a triple head-bashing on the desk. And you know what is funny, I program in C++ for more than 20 years. But because it is in a context where I'm not comfortable, I immediately put the blame on the hardware ;) \$\endgroup\$ – Martin Tétreault Apr 11 '16 at 20:11

It all comes down to Operator precedence.

In C/C++, != is evaluated before &. As a result, your condition is effectively:

if ( PINB & (2 == 0))

Which it should be clear that this is always going to be 0 - 2 == 0 is always 0.

You have two choices:

  1. Use something with a higher precedence in the if statement, for example ():

    if ( (PINB & 2) != 0 )

    Which will work as expected - the parenthesis are evaluated before the !=.

  2. Rely on the fact that any non-zero value is considered true:

    if (PINB & 2) //True is anything non-zero.
  • \$\begingroup\$ Shame on me... yes you are right. It was as simple as this... Lesson learned, check the code twice before putting the blame on the hardware. \$\endgroup\$ – Martin Tétreault Apr 12 '16 at 17:36

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.