18B20 驱动 MSP430

float get_temp(void);

void reset_18B20(void);

void send_18B20(char data);

unsigned int read_18B20(void);

#define ONE_WIRE_PIN BIT4

#define ONE_WIRE_IN P1IN

#define ONE_WIRE_OUT P1OUT

#define ONE_WIRE_DIR P1DIR

float get_temp(void)

{

    unsigned int temp;

    reset_18B20();

    send_18B20(0xcc);   //send CCH,Skip ROM command

    send_18B20(0x44);

    delay_us(100);

    reset_18B20();

    send_18B20(0xcc);   //send CCH,Skip ROM command

    send_18B20(0xbe);

    temp = read_18B20();

    return((float)temp/8.0);

}

void reset_18B20(void)

{

    ONE_WIRE_DIR |=ONE_WIRE_PIN;

    ONE_WIRE_OUT &= ~ONE_WIRE_PIN;

    __delay_cycles(500);

    ONE_WIRE_OUT |=ONE_WIRE_PIN;

    ONE_WIRE_DIR &= ~ONE_WIRE_PIN;

    __delay_cycles(500);

}

void send_18B20(char data)

{

    char i;

    for(i=8;i>0;i--)

    {

    ONE_WIRE_DIR |=ONE_WIRE_PIN;

        ONE_WIRE_OUT &= ~ONE_WIRE_PIN;

        __delay_cycles(2);

        if(data & 0x01)

        {

            ONE_WIRE_OUT |= ONE_WIRE_PIN;

        }

        __delay_cycles(60);

        ONE_WIRE_OUT |= ONE_WIRE_PIN;

        ONE_WIRE_DIR &= ~ONE_WIRE_PIN;

        data >>=1;

    }

}

unsigned int read_18B20()

{

    char i;

    unsigned int data=0;

    for(i=16;i>0;i--)

    {

    ONE_WIRE_DIR |= ONE_WIRE_PIN;

        ONE_WIRE_OUT &= ~ONE_WIRE_PIN;

        __delay_cycles(2);

        ONE_WIRE_OUT |=ONE_WIRE_PIN;

        ONE_WIRE_DIR &= ~ONE_WIRE_PIN;

        __delay_cycles(8);

        if(ONE_WIRE_IN & ONE_WIRE_PIN)

        {

            data |=0x8000;

        }

        data>>=1;

        __delay_cycles(120);

    }

    return(data);

}