Question

Port = 0x0055

A) Port &= 0xff0;

B) Port |= 15;  

C) Port = Port ^ 0x0005;

D) Port = ( ( Port &~(0x000f) ) | 0x0020 );  

Please explain how each logical opperator works and write out the results.

Answer 1

Given:
Port = 0x0055
   In decimal : 85
   In Binary: 1010101

A)  
   Port &= 0xff0;
       = Port = Port & 0xff0

       0xff0 = 4080 in decimal
               = 111111110000 in Binary

       Port & 0xff0 => 1010101 & 111111110000 = 1010000 in Binary

B)
   Port |= 15;
   Port = Port | 15

   15 = 1111 in Binary

   Port | 15 =>
       1010101 | 1111 = 1011111 => 95 in decimal

C)
   Port = Port ^ 0x0005;

   0x0005 => 5 in decimal => 101 in binary

   Port ^ 0x0005 = 1010101 ^ 101 => 1010000 => 80 in decimal

D)
   Port = ( ( Port &~(0x000f) ) | 0x0020 );

   0x000f = 15 in decimal = 1111 in binary
   ~(0x000f) = -16 in decimal = 11111111111111111111111111110000 in binary
   0x0020 = 32 in decimal = 100000 in binary

   ( Port &~(0x000f) => 1010101 & 11111111111111111111111111110000 = 80 in decimal = 1010000 in binary
   ( Port &~(0x000f) | 0x0020 => 1010000 | 100000 => 1110000 = 112 in decimal