Using a regiater like a bit in c programming?

[treez]

Hello,
We are using microchip XC8 free c compiler within mplab.x. We are programming PIC18F65K22.
We have two 8 bit registers dipsw2 and dipsw3 which are declared with the uint8_t type declaration.
Dipsw2 and dipsw3 only ever hold the value 0 or 1. (0x00 or 0x01)
Is the following type of comparison statement valid?

if (!dipsw2 && dipsw3) {currentint = 4;}

We believe this means, “if dipsw2 contains zero, and dipsw3 is non zero, then currentint register gets the value 4.”
This is treating the register rather like it’s a bit, but will this work?

 

[horace1]

in C 0 is false and any none 0 value is taken as true so you statement should work OK

you can always test it with a simple program using the MPLABX simulator

 

[treez]

thanks, but I am wondering, surely if dipsw3 contains 00000001, then !dipsw3 is 11111110 ...and not 00000000?
-its strange but asking the question kind of triggered this off in my head

 

[horace1]

! is logical NOT (if TRUE result becomes False) - if dipsw3 contains 00000001, then !dipsw3 is 0

you are thinkng of ~ which is bitwise NOT or complement

run a program like this in the simulator - try changing values see what happens

#include <xc.h>        /* XC8 General Include File */
#pragma config XINST = OFF 
void main(void)
{
    unsigned char dipsw2=0,  dipsw3=1,  currentint = 0, j;
    if (!dipsw2 && dipsw3) {currentint = 4;}
    j=!dipsw3;
    j=~dipsw3;

what do you think the result of this is?

    unsigned char dipsw2=0,  dipsw3=1;
   if (~dipsw2 & dipsw3) {currentint = 6;}

 

[treez]

thanks,
I think its 6, from your good advice

 

[horace1]

correct
in normal control structures one would use logical operators !, ||, &&

the bitwise operators ~ | & ^ are useful for testing individual bits in particular when checking the status registers of IO devices