3

I'm trying to manipulate the ports of Arduino using C code. I have attached an LED to pin 8 and a tact switch to pin 13 (with a pull down resistor). The code works fine, and the results are printed on the screen. So, when the button is pressed, the byte PINB & (1 << PB5) equals 32, or 0b00100000.

However, if I try to use

if( PINB &(1<<PB5) == 32){

or 

if( PINB &(1<<PB5) == 0b00100000){

the LED doesn't respond.

Here's the full code:

void setup() {
  DDRB |= 0b00011111; 
  Serial.begin(9600);
  }

void loop() {
  Serial.print("PINB &(1<<PB5)");
  Serial.println(PINB &(1<<PB5));

  if( PINB &(1<<PB5) ){
    PORTB |= (1<<PB0);
    }
  else{
    PORTB &= ~(1<<PB0);    
    }
  }

What am I missing?

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2
  • Are you saying the full code you've posted works, but it fails if you add == ...?
    – Peter Bloomfield
    Mar 17, 2015 at 15:45
  • That's right , it fails with == .
    – user3060854
    Mar 17, 2015 at 15:48

1 Answer 1

Reset to default
5

== has higher precedence than &, which means that your comparison will be performed incorrectly. But that doesn't matter, since you don't need to check if the port has a specific value, just if the appropriate bit is set.

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7
  • You are right. If I use my_byte = PINB &(1<<PB5) and if( my_byte = 0b00100000 ){ it works fine. Nevertheless, could you explain how the comparison with == and & works? Thank you.
    – user3060854
    Mar 17, 2015 at 15:55
  • 4
    Not really sure what needs to be explained. a & b == c is equivalent to a & (b == c).
    – Ignacio Vazquez-Abrams
    Mar 17, 2015 at 15:57
  • That's what I wanted to know. Thank you again.
    – user3060854
    Mar 17, 2015 at 16:00
  • 1
    I found another solution based on your last remark. if( (PINB &(1<<PB5) ) == 0b00100000){ works too
    – user3060854
    Mar 17, 2015 at 16:06
  • Eh. Like I said, you don't need to care about the exact value.
    – Ignacio Vazquez-Abrams
    Mar 17, 2015 at 16:08

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