This is our first program and it works quite well. If you load and run it you will see that the LEDS flicker when you change the light falling on the cell. Generally speaking, the less light that falls on the cell the more LEDS are lit, but because they are displaying binary this is not all that easy to see.

You should also notice that the program runs in reverse, in that the brighter the light the lower the number which is displayed. By the use of a torch or a desk lamp you should be able to get all the lights out but one. By covering the sensor you should be able to get all the leds to illuminate.

Exercise 10.1

/*  EX 10.1 Binary Light Display            */
/*  Needs Port A pin 0 as an analogue input */
/*  David Miles April 2006                  */

#include <system.h>

void setup_hardware (void)
{

    /* set all of PORTB for output   */ 
    TRISB = 0x00 ;

    /* bits 1-3 of PORTA for output  */
    /* using bit 0 for analogue      */
    /* input                         */
    TRISA = 0xf1 ;

    /* select A0 for analogue input  */
    ADCON0 = 0x00 ;

    /* set for right justified value */
    ADCON1 = 0x80 ;

    /* Just A0 in analogue mode      */
    ANSELA = 0x01 ;
}


void main ( void )
{

    unsigned char i, h, l ;

    setup_hardware () ;

    while (1)
    {
        /* enable the converter and start    */
        /* a conversion                      */
        ADCON0 = 0x05 ;

        /*  spin while the conversion runs   */
        while ( ADCON0 & 0x04 );

        /* read the high byte                */
        h = ADRESH;

        /* read the low byte.                */
        l = ADRESl;

        /* display the result.               */
        PORTB = l ;
        PORTA = h * 2 ;
    }
}