File content as of revision 0:d0b35e0b4294:

#include "mbed.h"

// DS18B20 converted to run on mbed

#define TEMP_PIN  p20

Serial pc(USBTX, USBRX); // tx, rx

DigitalInOut temperature_pin(TEMP_PIN);

void OneWireReset() { // reset.  Should improve to act as a presence pulse
    temperature_pin.output();
    temperature_pin = 0;     // bring low for 500 us
    wait_us(500);
    temperature_pin.input();
    wait_us(500);
}

void OneWireOutByte(unsigned char d) { // output byte d (least sig bit first).
    for(int n=8; n!=0; n--) {
        if ((d & 0x01) == 1) { // test least sig bit
            temperature_pin.output();
            temperature_pin = 0;
            wait_us(5);
            temperature_pin.input();
            wait_us(60);
        } else {
            temperature_pin.output();
            temperature_pin = 0;
            wait_us(60);
            temperature_pin.input();
        }

        d=d>>1; // now the next bit is in the least sig bit position.
    }

}

unsigned char OneWireInByte() { // read byte, least sig byte first
    unsigned char d = 0, b;
    for (int n=0; n<8; n++) {
        temperature_pin.output();
        temperature_pin = 0;
        wait_us(5);
        temperature_pin.input();
        wait_us(5);
        b = temperature_pin;
        wait_us(50);
        d = (d >> 1) | (b << 7); // shift d to right and insert b in most sig bit position
    }
    return d;
}

int main() {
    int HighByte, LowByte, TReading, SignBit, Tc_100, Whole, Fract;
    pc.printf("mbed 1 wire interface simple test!\r\n");
    temperature_pin.output();
    temperature_pin = 0;
    temperature_pin.input();  // sets the digital pin as input (logic 1) make sure external pullup resistor 4K7
    wait(1);
    pc.printf("temperature measurements:\r\n");

    while (1) {
        OneWireReset();
        OneWireOutByte( 0xcc);  //Skip ROM command
        OneWireOutByte( 0x44); // perform temperature conversion, strong pullup for one sec

        OneWireReset();
        OneWireOutByte( 0xcc);
        OneWireOutByte( 0xbe);   //Read Scratchpad

        LowByte = OneWireInByte();
        HighByte = OneWireInByte();
        TReading = (HighByte << 8) + LowByte;
        SignBit = TReading & 0x8000;  // test most sig bit
        if (SignBit) { // negative
            TReading = (TReading ^ 0xffff) + 1; // 2's comp
        }
        Tc_100 = (6 * TReading) + TReading / 4;    // multiply by (100 * 0.0625) or 6.25

        Whole = Tc_100 / 100;  // separate off the whole and fractional portions
        Fract = Tc_100 % 100;

        if (SignBit) { // If its negative
            pc.printf("-");
        }
        pc.printf("%d", Whole);
        pc.printf(".");
        if (Fract < 10) {
            pc.printf("0");
        }
        pc.printf("%d", Fract);
        pc.printf("\r\n");
       
        wait(5);         // 5 second delay.  Adjust as necessary
    }
}