I have a problem. I am programming a PIC. In the program I load a value from portb to the register TANKOD. The value from portb tell me wich button that is pressed down on a keypad. If button 3 is pressed, 3 will be the value of portb.

 

My problem is that the keypad use "negative logic" or something like that. A 0 is a 1 and a 1 is a 0. So i want to invert the register.

 

11111100    =>    00000011

 

 

Any Idea how I can do this in a easy way. 

 

Something like this should work for you.

 

movlw    .255

xorwf    portb,w

movwf    tankod