DS18B20 and PIC18F4550

[sjohansson]

Hi

I'm trying to get the temperature values from a DS18B20 but it seems like I receive only the lower 6 bits. Right now I have 101110 wich is 2.8750.
When I touch the sensor it will increase the values, like 110011 wich is 3.1875. So I think the sensor is ok but for some reason it doesnt give me all bits. I use a 4.7k pull up.

My program looks like this:



ADCON1 = %00001111
DEFINE OSC 48
DEFINE LOADER_USED 1
DEFINE RESET_ORG 800h ' For Microchip USB Bootloader
DEFINE INTERRUPT_ORG 808h ' For Microchip USB Bootloader
Define LCD_DREG PORTA
Define LCD_DBIT 0
Define LCD_RSREG PORTA
Define LCD_RSBIT 4
Define LCD_EREG PORTB
Define LCD_EBIT 3
DEFINE LCD_BITS 4
DEFINE LCD_LINES 2
DEFINE LCD_RWREG PORTA
DEFINE LCD_RWBIT 2


DQ VAR PortC.0 ' One-wire Data-Pin "DQ" on PortC.0
Busy VAR BIT ' Busy Status-Bit
R_Temp VAR WORD ' RAW Temperature readings

Low PORTA.5 ' LCD R/W line low (W)

MainProgram:
OWOUT DQ, 1, [$CC, $44] ' Skip ROM search & do temp conversion
Wait_Up:
OWIN DQ, 4, [Busy] ' Read busy-bit
IF Busy = 0 THEN Wait_Up ' Still busy..?, Wait_Up..!
OWOUT DQ, 1, [$CC, $BE] ' Skip ROM search & read scratchpad memory
OWIN DQ, 2, [R_Temp.Lowbyte, R_Temp.Highbyte]' Read two bytes / end comms
lcdout $fe,1,"High= ",bin R_Temp.Highbyte," Low= ",bin R_Temp.Lowbyte
GOTO MainProgram
END



And it gives me "High= 0 Low= 101110" on the LCD.
I have two sensors to test with and they act the same way.
What can be wrong here? I tried to take the code direct from here: http://www.rentron.com/PicBasic/one-wire3.htm
But no success. It just print +2.8750 on LCD.

Thanks in advance.

Stefan.

[DynamoBen]

This may seem like an obvious thing but several ppl including myself made this mistake.

On the datasheet look at the not below the pinout, it says "Bottom View" which is opposite from what you may be used to.

Vcc and Gnd may be flipped. When this happens they seem to be functioning but that isn't the case.

Seriously start there.

[sjohansson]

Hm... My misstake... I thought I could see a "B" In DS18B20 but there is no "B" so the resolution of the sensor is 0.5degrees instead of 0.0625degrees.
101110 = 23,0Deg and 110011 = 25,5Deg.

/Stefan.