DS18B20 + OneWire + PIC18F4550 code query

[Giedrius Stasiulis]

Hello all,

In the last three days I was struggling to read temperature data from a single DS18B20 when using non-parasitic OneWire protocol and a PIC18F4550. Finally I had a break-trough (at least I think I have), when I decided to take baby steps and : 1. Read a presence pulse; 2. Read device family code; 3. Attempt to read temperature data. So far points 1 and 2 were accomplished successfully, I was able to read the presence pulse (0) and a family code (0x28). But the last point, I am still struggling bad. I understand that in order to read temperature values, I first need to write a command to convert temperature (0x44), then reset the OneWire, give a 0.75s delay for the conversion to be completed, and then write to the scratchpad 0xBE to read from the register. I've tried combining the codes I found in maxim website and as well some other codes I found all over the web. LCD now displays Temperature: 11, when my room temperature is currently ~27 degrees C. Please can someone check my codes to see whether there is an issue somewhere? Thanks!
 
DS18B20 config.h:

#define _XTAL_FREQ 8000000

#define Data_pin RB2

#define Data_bus TRISB2

#define Skip_ROM 0xCC                // 0b11001100

#define Convert_temperature 0x44    // 0b01000100

#define Read_scratchpad 0xBE            // 0b10111110

#define Read_deviceFamily 0x33



int OneWire_reset()

{

Data_bus = 0;        //Set as output

Data_pin = 0;        //Drive Low

__delay_us(480);

Data_bus = 1;        //Release, Set back as input

__delay_us(70);



if (Data_pin == 0)        // Sample bus

{

__delay_us(410);

return 0;        // Device present

}

else

{

__delay_us(410);

return 1;        // No device present

}

}



int OneWire_readByte(void)

{

int l, result = 0;

for(l=0;l<8;l++)

{

result >>= 1;

if(OneWire_readBit())

result |= 0x80;

}

return result;

}



int OneWire_readBit(void)

{

unsigned int Read_state = 0;



Data_bus = 0;        //Set as output

Data_pin = 0;        //Drive low

__delay_us(6);

Data_bus = 1;        //Release, set as input

__delay_us(9);

Read_state = Data_pin;



return Read_state;

}



void OneWire_writeBit(unsigned int b)

{

Data_bus = 0;        //Set as output

Data_pin = 0;        //Drive low



if(b == 1)

{

__delay_us(3);

Data_bus = 1;    //Release, set as input

__delay_us(62);

}

else

{

__delay_us(57);

Data_bus = 1;    //Release, set as input

__delay_us(7);

}

}



void OneWire_writeByte(unsigned int data)

{

int l;

for(l=0;l<8;l++)

{

OneWire_writeBit(data & 0x01);

data >>= 1;

}

}

 

And the main code:

#define _XTAL_FREQ 8000000

#include <xc.h>

#include <stdio.h>

#include "LCD_4bit_config.h"

#include "DS18B20_config.h"

#include "delay.h"



OneWire_init()

{

int i;

char buf1[10];

char buf2[10];



LCD_setCursor(1,1);

LCD_writeString("Presence:");



i = OneWire_reset();



sprintf(buf1,"%d",i);

LCD_setCursor(2,1);

LCD_writeString(buf1);



delay_ms(3000);

LCD_clr();



OneWire_reset();



LCD_setCursor(1,1);

LCD_writeString("Device family:");



OneWire_writeByte(Read_deviceFamily);



i = OneWire_readByte();



sprintf(buf2,"%d",i);

LCD_setCursor(2,1);

LCD_writeString(buf2);



delay_ms(3000);

LCD_clr();



OneWire_reset();

}



void main()

{

char temp_lsb,temp_msb,temp;



char buf3[10];



char getBit[10];



int k;



OSCCON = 0b11110010;    // Set PIC18F4550 internal oscillator at 8MHz



ADCON1 = 0x0F;            // Set all pins as digital I/O

CMCON = 0x07;             // Set all comparators as digital I/O



LATD = 0;			    // Clear port D

TRISD = 0b00000000;		// Set all port D pins as digital outputs



LATB = 0;

TRISB = 0x00;



LCD_init();				// Initialize LCD

OneWire_init();



while(1)

{



if (!OneWire_reset())

{

LCD_setCursor(1,1);

LCD_writeString("Temperature:");



OneWire_writeByte(Skip_ROM);

OneWire_writeByte(Convert_temperature);



OneWire_reset();

delay_ms(750);



OneWire_writeByte(Skip_ROM);

OneWire_writeByte(Read_scratchpad);



for (k=0;k<9;k++)

{

getBit[k] = OneWire_readByte();

}



temp_msb = getBit[1];

temp_lsb = getBit[0];



temp = (temp_msb <<  + temp_lsb;



temp = temp >> 4;



sprintf(buf3,"%d",temp);

LCD_setCursor(2,1);

LCD_writeString(buf3);



delay_ms(1000);

}

}

}

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