sharp.c

Go to the documentation of this file.

/*
 * Control code for Sharp GP2D120 Distance Measuring Sensor
 *
 * (c) 2007 by Matthias Arndt <matthias.arndt@tu-clausthal.de>
 *
 * sensor analog input connected to P1.0
 * sensor activation via P3.2
 *
 * Timer 1 is used to count 2 ticks of 25 ms to achieve a pause of 50ms when
 * the Sharp is about to be polled
 */
#include "t89c51cc02.h"
#include "datatypes.h"
#include "adc.h"
#include "sharp.h"

volatile bit sharp_ready; 
volatile bit wait_bit;  

void Sharp_init()
{
        ADCF |= 0x01;   /* program P1.0 for analogue input */
        Sharp_PowerOff();
        /* Sharp waiting timer is programmed upon poweron of Sharp sensor */
}

void Sharp_TimerInit()
{
        TR1=0;          /* stop Timer 1 */
        TMOD = (TMOD & 0x0F); /* leave Timer 0 intact */
        TMOD |= 0x10;   /* Timer 1 Mode 1 */
        TF1=0;          /* clear timer flag */

        /* initial timing value */
        TH1=SHARP_TIMER_RELOAD_H;
        TL1=SHARP_TIMER_RELOAD_L;
        
        wait_bit=1;
        sharp_ready=0;
        TR1=1;          /* start Timer 1 */
        ET1=1;          /* activate Timer 1 interrupt */
}

void Sharp_Timer_interrupt(void) interrupt 3 using 2
{
        if(wait_bit)
        {
                /* reload Timer 1 once */
                TR1=0;
                TH1=SHARP_TIMER_RELOAD_H;
                TL1=SHARP_TIMER_RELOAD_L;
                TR1=1;
                TF1=0;          /* acknowledge Timer 0*/
                wait_bit=0;     /* next Timer ISR invocation will enable Sharp */
        } else {
                sharp_ready=1;
                TF1=0;
                ET1=0; /* cut off Sharp Timer ISR as the Sharp is ready to be read to free CPU time */
        }
}

WORD Sharp_read()
{
        /* wait until Sharp has been powered on */
        if(!SHARP_PWRCTL)
        {
                /* Sharp is off */
                return(0xffff);
        } else {
                while(!sharp_ready);    /* wait until Sharp is ready...*/
                return(ADC(0));
        }
}

---