DS18B20 one wire communication with PIC

[diamadiss]

Hello,
I am using for first time one wire protocol. I searched on the internet and I found some functions but I can't manage them. I found a code for PIC in assembly for one wire communication at the below link and I converted to C language but doesn't work. Also, I saw on DS18B20 datasheet at "function command set" and I change the values of command that I send but it stills doesn't work. I want to use DS18B20 with parasite power on C18 compiler with PIC18F2550. Could anyone help me to solve this.
  
One wire communication application note : http://www.maximintegrated.com/app-notes/index.mvp/id/2420

[pickit2]

a site I visit from time to time
http://www.pic_examples.byethost3.com/DS18B20.html

[xpress_embedo]

I had made a project based on One-Wire Protocol.
I used DS1822 and PIC16F877A Micro-Controller

Hi-Tech C Compiler v9.83

Please find the attached the link to download the project with proteus simulation file.

[jamesbond]

I use these functions for all my one wire applications.
May be you can use it.

[diamadiss]

Hello,
Thanks for replies. I would to create my own function so I can to understand one wire communication with parasite power. Please, could anyone guide my to fix it? Thanks.

[flo0319]

1-wire protocol is based on time slots, so you need to make samples for bits when you are sure that the line is stabilized, and also you need to implement an external filter to eliminate parasites  from the line. in general you need to put a delay between normal time (1us or 5us)  and the moment when you read value form pin


Be careful with the pull-up resistor from line, at a dsPIC just with internal pull-up enabled worked 

[diamadiss]

I made some changes according to operation example from DS18B20 datasheet. But now always it shows on display the value "-1". Please could anyone see the attached picture which shows the "operation example" from datasheet because I think that I must sent wrong data. Also, I have attached my code so to see it.
  
Datasheet DS28B20 :  
http://datasheets.maximin....com/en/ds/DS18B20.pdf  
  
1-Wire® Communication with a Microchip PICmicro Microcontroller :
http://www.maximintegrate...otes/index.mvp/id/2420
  

[flo0319]

Hi again,
you need to make some changes in your code :
look at my code first:

Code:

void prvWireInit(void)
{	
	CNPU1=64; // for pull-up resistors 
	WireDir=1;
	WirePin=1;
};
void prvWireReset(void)
{
	WireDir=0;
	WirePin=0;
	delayus(550); // more then 500 
	WirePin=1;
	WireDir=1;
	delayus(70);
};

int prvWirePresence(void)
{	int i;
	int Bit=0;
	WireDir=1;
	for(i=480;i>0;i--)
	{
	delayus(1);
	if (WirePin==0) Bit=1;
	};
	return Bit;
};

void prvWireSendBit(unsigned portCHAR Bit)
{
	WireDir=0;
	WirePin=0;
	delayus(2);
	WirePin=Bit;
	delayus(TSlot); // 60us
	WireDir=1;
	delayus(2);
};

portCHAR prvWireGetBit(void)
{	portCHAR Bit;
	WireDir=0;
	WirePin=0;
	delayus(2);
	WireDir=1;
	delayus(20);
	Bit=WirePin;
	delayus(100); 
	return Bit;
};

void prvWireWriteByte(unsigned portCHAR Byte)
{
	int i;
	for (i=0;i<8;i++)
	{ 
	prvWireSendBit( Byte&0x01);
	Byte=Byte>>1;
	};
};

char  prvWireReadByte(void)
{
	int i;
	char Byte;
	Byte=0;
	for(i=0;i<8;i++) 
	Byte=Byte|((1&prvWireGetBit())<<i);
	return Byte;
};

it's better in this case to use PORT register and not LAT register for read and write to pin.

you need to insert more delays in your code, and very important is how receive the presence impulse from sensor.

also look at how is initiate a communication between mcu and sensor (is not for parasite power but is similar)

Code:

//reinitializare si startare citire temp	
				prvWireReset();  
				prvWirePresence();
				prvWireWriteByte(0xCC);
				prvWireWriteByte(0x44);

				vTaskDelay(300); // 300ms delay (but this can be a short time >10ms )

				//comanda citire temperatura
				prvWireReset();
				prvWirePresence();
				delayus(70);
				
				prvWireWriteByte(0xCC);
				prvWireWriteByte(0xBE);

				WireDir=0;
				WirePin=0;

				test1=prvWireReadByte();
				delayus(70);
				test2=prvWireReadByte();
				vTemp=(unsigned int)(test2<<8)+ (unsigned int) test1;
				prvWireReset();
				prvWirePresence();

 

after reset you need to wait 480us for presence impulse response

you have on display -1 because your data is 0xFF  (from pull-up) and "%d" is for signed decimal , for unsigned you need to use %u . 

[diamadiss]

Hello,
I am trying to make compile in your code but compile failed (syntax error). I have attach a txt with your code with my code. Thanks a lot for your help.

[flo0319]

It's normal to have this problem :

add to your code this:

#define delayus(x) _delay((unsigned long)((x)*(_XTAL_FREQ/4000000.0)))
#define delayms(x) _delay((unsigned long)((x)*(_XTAL_FREQ/4000.0)))

#define WirePin        PORTAbits.PORTA0 // or _PA0
#define WireDir        TRISAbits.TRISA0         // "DQ_TRIS = 0;" This must included in the main program
 
and change:

delayus(TSlot); // 60us with delayus(60);

vTaskDelay(300); // 300ms delay (but this can be a short time >10ms ) with
delayms(300); // 300ms delay (but this can be a short time >10ms )

delete from prvWireInit(void) CNPU1 = 64;

and declare test1,test2 as unsigned char and vTemp as integer

if other errors occur , you can manage it by yourself

until to go in while(1), call prvWireInit() to initiate the port pin

[ehnonymouse]

I don't know whether this will help, but this is some sample code I modified to read the serial number from a DS2411. It's for the MPLAB C30 compiler and a PIC24. Tested, and working in the application.

[diamadiss]

I magage to make compile with flo0319 code but doesn't work. Always it shows on display the value 255. Also, I replace "portCHAR" with "char" so to make a successful compile. I see on datasheet of "DS18B20 operation example 2" which is for parasite power that we don't send all the commands. Is this possible to be the cause of the problem? In txt file I have attached the code which it does succesful compile. Thanks.

[LithiumOverdosE]

Check out Dallas 1-Wire application notes. They enclosed C code that can be easily ported to PIC compilers with modification of bit read/write procedures.

Also check out AVR318 App Note.

[flo0319]

diamadiss, tell me how you have connected your ds18b20 to uC and try to communicate with it in normal power mode
after you can view that your sensor work(with external power) you can change and can try to communicate with it in parasite mode
if you can make a picture with your schematic and hardware we can view if is something wrong there

[diamadiss]

I use it without parasite power for now but it doesn't work. In picture you can see my schematic.

[flo0319]

your problem is form pin configuration

Note: On a Power-on Reset, RA5 and RA3:RA0
are configured as analog inputs and read
as ‘0’. RA4 is configured as a digital input.

you need to configure RA0 as digital pin  (after reset this pin si analog)

ADCON1 = 0x0F ; // to do all pins digital
this instruction you need to add on initiation (in main() )

[diamadiss]

I have already add these "commands" on my code but didn't work.

    ADCON0 = 0x00;
    ADCON1 = 0x0F;
    CMCON = 0x07;                //Disable Comporators

[flo0319]

I think that your sensor is the problem, try to change with another one

[diamadiss]

I replace the sensor with new but it stills show 255.

[metal]

Your sensor has P at the end? Like in DS18B20P?

[diamadiss]

Yes, the code is "DS18B20 + PAR"

[metal]

The reason for your reading is that after you issue the read command, you are not pulling the pin connected to DS18B20P high, it really needs a strong pull and can be done by setting the pin itself high and as an output, which means you are not providing supply for the DS18B20P. Look at this:

Code:

void therm_read_temperature(int16_t *temperature){
	//Reset, skip ROM and start temperature conversion
	therm_reset();
	therm_write_byte(THERM_CMD_SKIPROM);
	cli();
	therm_write_byte(THERM_CMD_CONVERTTEMP);
	//Wait until conversion is complete
#ifdef ONEWIRE_USE_PARASITIC_POWER
	THERM_HIGH();  
	THERM_OUTPUT_MODE();
	sei();
	//THERM_INPUT_MODE();
	_delay_ms(751);	
	//THERM_INPUT_MODE();
#else	
	THERM_INPUT_MODE();	
	sei();
	while(!therm_read_bit());
#endif
	//Reset, skip ROM and send command to read Scratchpad
	therm_reset();
	therm_write_byte(THERM_CMD_SKIPROM);
	therm_write_byte(THERM_CMD_RSCRATCHPAD);
	//Read Scratchpad (only 2 first bytes)
	*temperature = therm_read_byte();
	*temperature |= therm_read_byte() << 8;
	therm_reset();
}

After issuing "therm_write_byte(THERM_CMD_CONVERTTEMP);", you have to ensure that you controller has done its homework:

// Write 1 to pin connected to DS18B20P
THERM_HIGH();
// Pin is output
THERM_OUTPUT_MODE();


Also ensure that interrupts are disables before you execute the above two operations. Look at your code, and seek where you should do this modification.

[diamadiss]

I make high for 100us the pin which connected DS18B20 and I disable all interupts "INTCONbits.GIE = 0; // Disable global interrupts" but it stills show the value "255". I have attached my code so to see where I make the DS18B20 pin high. Also, I tried to work with xtal 4MHz instead 20MHz but nothing. Thanks.

[metal]

it should be high for 750ms, not 100us, look at my code: _delay_ms(751);

[flo0319]

diamadiss, have you an oscilloscope or something to view exactly what is happened on this line?