I am using a push button to control something on a PIC16F887 but as soon as I let go of the button it reverse back. If I have a variable called switch, how to I toggle it between 1 and 0 each time RB0 is triggered? I need some sort of latch in C

 

Depends on the type of variable "switch" is defined as. I am not familiar with C conventions, but something like the following will work with logical variables:
Switch = ! Switch
Or mathematically, you can use the following equation if you have the absolute value function available :
Switch = | Switch - 1 |

 

Use som variable that is changed each time the button is pressed. Then let this variable controll the direction. Given that then RB0 button goes high then pressed. I think this pseudo code will do the trick. You have to code it proper by your self

 char dir_var
 if (RB0)
    {
       dir_var=!dir_var//flip the dir_var variable
        while(RB0)// wait and do nothing until the button is released
      }
       //Check the dir_var variable
       //in code to find out which
       // way to rotate
       if(dir_var)
          {
           //rotate left
            }
      if(!dir_var)
          {
           //rotate right
            }

 

I also found out that the RB0 pin, is also the interrupt pin on your MCU. And I am quite sure the interrupt pin can be set up to be edge trigged.

 

An interrupt is probably one of the worst ways to sense a physical switch as it is just TOO FAST. Switches have a bounce,so when you press them they give multiple change signals, which fire multiple interrupts.

Now I happen to typically use an interrupt to sense my push buttons, but the ISR is called off a timer because I sample the buttons at a slow rate (10-25 ms), and make sure I get 2 readings the same before I declare it as a change.

To toggle a pin needs code of a form such as this:

    while(1)
    {
        while(button == OFF);
        while(button == ON) Pin = 1 ;
        while(button == OFF);
        while(button == ON) Pin = 0 ;
    }

Do note the 4 internal while loops trap the program when the button is either not pressed or pressed. That keeps the pin from either continuously changing or releasing with the button.

Also note *real* code would have other functions, but that's how a button test loop could work.

 

Ok I attempted a latch. Its kinda working, but for some reason there is a problem with the do while loop. The LED keeps moving back and forth between two positions whilst the button is pushed down when I thought it would just either free or keep going in one direction

/*
* File:   Lab4inC.c
* Author: David Baratheon
*
* Created on 18 June 2013, 20:45
*/


#include <xc.h>
#define _XTAL_FREQ 8000000 //Using 8MHz clock speed

void main(void)
{

//Declaring and Defining Variables

char Blink;
char Counter;
char Switch;

Blink = 0x01;
Counter = 0x00;
Switch = 0x00;

//Configuring the Input and Output Ports


PORTD = Blink;
ANSELH = 0b00000000;
ANSEL = 0b00000000;
TRISD = 0x00;
TRISB = 0b11111111;
TRISA = 0b11111111;

//main program

    while(1)
    {
        //Stimulus Dependant Rotating Bit
        //Bit shifting left
    if(!Switch)
        {

            if(!RB0)
            {
                __delay_ms(250); // request a delay

                if(!RB0)
                {
                Switch = !Switch;
                do{ __delay_ms(25); }
                while(RB0=0);
                }
            }


            if(Counter<7)
            {
                Blink = Blink << 1;    //
                                PORTD=Blink;
                                __delay_ms(250); // request a delay
                Counter++ ;
                //CLRWDT();
            }

            else
            {
                Blink = 0x01;    //
                                PORTD=Blink;
                                __delay_ms(250); // request a delay
                Counter = 0x00;
                //CLRWDT();
            }
        }

//Bit shifting right

    if(Switch)
        {

            if(!RB0)
            {
                __delay_ms(250); // request a delay

                if(!RB0)
                {
                Switch = !Switch;
                do{ __delay_ms(250); }
                while(RB0=0);
                }
            }
            if(Counter>0)
            {
                Blink = Blink >> 1;    //
                                PORTD=Blink;
                                __delay_ms(250); // request a delay
                Counter = Counter - 1 ;
                //CLRWDT();
            }

            else
            {
                Blink = 0x80;    //
                                PORTD=Blink;
                                __delay_ms(250); // request a delay
                Counter = 0x07;
                //CLRWDT();
            }
        }

    }
}

 

Actually its ok, all I needed to do was have two equals signs.

Ok so project finished, thank you very much for your help everyone, I learned a lot from it and had fun. I hope I can get involved in some online projects with others to learn more as my knowledge grows.

Thanks and best wishes everyone