int i=0;
DDRD = 0xff;
PORTC = 0xff;  
while (1) 
    if(PINC5 == 1)

I have been trying to figure out why the comparison of PC5 pin of PORTC with 1 yields False everytime. I have activated the "pull up" resistor for every pins of Port C. But still, when I compare the PC5 to 1, I don't get the expected result.

I know the proper way is to do the comparison using the bit-masking.

if((PORTC &(1<<PORTC5))==0).

But I can't figure out why the code presented above doesn't work.

I feel like I am missing some fundamentals in bit-wise operators but can't figure out what exactly. Thank you!!

The datasheet of Atmega 328P says the following:

All registers and bit references in this section are written in general form. A lower case “x” represents the numbering letter for the port, and a lower case “n” represents the bit number. However, when using the register or bit defines in a program, the precise form must be used. For example, PORTB3 for bit no. 3 in Port B, here documented generally as PORTxn.

  • \$\begingroup\$ What is the definition of PINC5? \$\endgroup\$
    – Long Pham
    Commented Jan 20, 2020 at 16:24
  • \$\begingroup\$ PINC5 is just a constant which indicated which bit of PORTC matches PC5. It is not the value of that bit. \$\endgroup\$
    – jcaron
    Commented Jan 20, 2020 at 16:24
  • 1
    \$\begingroup\$ Where is it defined? \$\endgroup\$
    – Andy aka
    Commented Jan 20, 2020 at 16:29
  • 2
    \$\begingroup\$ Look here github.com/vancegroup-mirrors/avr-libc/blob/master/avr-libc/… and see that PINC5 is a constant number equal to 5. And to read pin state you need to use a PINC register in your case. \$\endgroup\$
    – G36
    Commented Jan 20, 2020 at 16:42

1 Answer 1


PINC5 and PORTC5 are defines that equate to 5. So the code does not read status of pins of IO port C at all to get the status of the bits, it is just comparing if number 5 is number 1 and it never is. Also, PORTC is the output data register. If you want to read status of a pushbutton, you must read PINC register.

  • \$\begingroup\$ Got it!! Thanks a lot @Justme \$\endgroup\$
    – G-aura-V
    Commented Jan 20, 2020 at 16:48
  • \$\begingroup\$ @JuneStar_2918 I use ARM, not AVR, but with my compiler, with the way the built in register definitions are defined, I can't actually go "if(Register->Bit == 1)" or "if(Register->Bit == true)". I actually have to go "if(Register->Bit)" or "if(!Register->Bit)". Just so you know what's out there. \$\endgroup\$
    – DKNguyen
    Commented Jan 20, 2020 at 19:06

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