DS18B20 1-wire Driver for CCS C

I got my hands on a few of these DS18B20 1-wire digital temperature sensors. They’re really awesome. They’re small, easy to work with, and they run on the 1-wire bus which means they can run on a minimum of two wires. However, I found it easier to just run these devices with 3 lines: +5V, GND, Bus – saves a lot of design complexity.

I found a few good 1-wire drivers for CCS C (especially for these devices):

DS18S20 & DS18B20 Codes

One DS18B20 in powered mode

dallas onewire primitives library and ds1822 driver code

I then took ideas from them and made my own little driver. Some of the code is copied, some of it isn’t. Here it is:

main.c

#include "main.h"
#include "1wire.c"
#include "ds1820.c"

float value = 0.0;

void main() {
    setup_adc_ports(NO_ANALOGS|VSS_VDD);
    setup_adc(ADC_OFF);
    setup_spi(SPI_SS_DISABLED);
    setup_timer_0(RTCC_INTERNAL|RTCC_DIV_1);
    setup_timer_1(T1_DISABLED);
    setup_timer_2(T2_DISABLED,0,1);    
    setup_oscillator(OSC_8MHZ);
    setup_uart(9600);
    
    delay_ms(1000);
    
    printf("Starting...\t\n");
    while(TRUE) {        
        value = ds1820_read();
        printf("%f\t\n", value);        
    }
}

main.h

#ifndef MAIN_H
#define MAIN_H

#include <16F690.h>
#device adc=8

#FUSES NOWDT                     //No Watch Dog Timer
#FUSES INTRC_IO                  //Internal RC Osc, no CLKOUT
#FUSES NOPROTECT                 //Code not protected from reading
#FUSES NOBROWNOUT                //No brownout reset
#FUSES NOMCLR                    //Master Clear pin used for I/O
#FUSES NOCPD                     //No EE protection
#FUSES PUT                       //Power Up Timer
#FUSES IESO                      //Internal External Switch Over mode enabled
#FUSES FCMEN                     //Fail-safe clock monitor enabled

#use delay(clock=8000000)
#use rs232(baud=9600, parity=N, UART1, bits=8, stop=1)

#endif /*MAIN_H*/

1wire.c

#ifndef ONE_WIRE_C
#define ONE_WIRE_C

/*
 * One wire (1-wire) driver for CCS C compiler. Suitable for use with devices
 * such as the DS18B20 1-wire digital temperature sensor.
 */

#define ONE_WIRE_PIN PIN_C5

/*
 * onewire_reset()
 * Description: Initiates the one wire bus.
 */
// OK if just using a single permanently connected device
void onewire_reset() {
    output_low(ONE_WIRE_PIN);       // pull the bus low for reset
    delay_us(500);
    output_float(ONE_WIRE_PIN);     // float the bus high
    delay_us(500);                  // wait-out remaining initialisation window
    output_float(ONE_WIRE_PIN);
}


/*
 * onewire_write(int8 data)
 * Arguments: a byte of data.
 * Description: writes a byte of data to the device.
 */
void onewire_write(int8 data) {
    int8 count;

    for(count = 0; count < 8; ++count) {
        output_low(ONE_WIRE_PIN);
        delay_us(2);                // pull 1-wire low to initiate write time-slot.
        output_bit(ONE_WIRE_PIN, shift_right(&data, 1, 0)); // set output bit on 1-wire
        delay_us(60);               // wait until end of write slot.
        output_float(ONE_WIRE_PIN); // set 1-wire high again,
        delay_us(2);                // for more than 1us minimum.
    }
}

/*
 * onewire_read()
 * Description: reads and returns a byte of data from the device.
 */
int onewire_read() {
    int count, data;

    for(count = 0; count < 8; ++count) {
        output_low(ONE_WIRE_PIN);
        delay_us(2);                // pull 1-wire low to initiate read time-slot.
        output_float(ONE_WIRE_PIN); // now let 1-wire float high,
        delay_us(8);                // let device state stabilise,
        shift_right(&data, 1, input(ONE_WIRE_PIN)); // and load result.
        delay_us(120);              // wait until end of read slot.
    }
    return data;
} 

#endif /*ONE_WIRE_C*/

ds1820.c

#ifndef DS1820_C
#define DS1820_C

#include "1wire.c"

float ds1820_read();
void ds1820_configure(int8 TH, int8 TL, int8 config);

/*
 * ds1820_read()
 * Description: reads the ds18x20 device on the 1-wire bus and returns
 *              the temperature
 */
 
float ds1820_read() {
    int8 busy=0, temp1, temp2;
    signed int16 temp3;
    float result;
    
    //ds1820_configure(0x00, 0x00, 0x00);     //9 bit resolution

    onewire_reset();
    onewire_write(0xCC);            //Skip ROM, address all devices
    onewire_write(0x44);            //Start temperature conversion

    while(busy == 0)                //Wait while busy (bus is low)
        busy = onewire_read();

    onewire_reset();
    onewire_write(0xCC);            //Skip ROM, address all devices
    onewire_write(0xBE);            //Read scratchpad
    temp1 = onewire_read();
    temp2 = onewire_read();
    temp3 = make16(temp2, temp1);
 
    //result = (float) temp3 / 2.0;   //Calculation for DS18S20 with 0.5 deg C resolution
    result = (float) temp3 / 16.0;    //Calculation for DS18B20
 
    delay_ms(200);
    return(result);
}

/*
 * ds1820_configure(int8 TH, int8 LH, int8 config)
 * Description: writes configuration data to the DS18x20 device
 * Arguments: alarm trigger high, alarm trigger low, configuration
 */

void ds1820_configure(int8 TH, int8 TL, int8 config) {
    onewire_reset();
    onewire_write(0xCC);            //Skip ROM, address all devices
    onewire_write(0x4E);            //Write to scratchpad
    onewire_write(TH);
    onewire_write(TL);
    onewire_write(config);
}

#endif /*DS1820_C*/

All you have to do is set the define to the appropriate pin you’re using for the 1-wire bus. Remember to attach a 4.7k pullup resistor on the bus to VDD. The value of the pullup resistor is not critical. If I remember correctly, I tested resistors anywhere from 1k to 10k and they worked fine. If not, just stick with the 4.7k pullup as recommended in the DS18B20 datasheet.