readtemp12

ReadTemp12

Syntax:

    byte_var = ReadTemp12

Command Availability:

Available on all microcontrollers.

Explanation:

ReadTemp12 is a function that returns the raw value of the sensor. The following two lines must be included in the Great Cow BASIC source file.

    #include <DS18B20.h>
    #define DQ PortC.3 ; change port configuration as required

Reads sensor and stores in output variable. The conversion takes up to 750ms. Readtemp12 carries out a full 12 bit conversion.

This command is for advanced users only. For standard ‘whole degree’ data use the Readtemp command.

The temperature is read back as the raw 12 bit data into a word variable (0.0625 degree resolution). The user must interpret the data through mathematical manipulation. See the DS18B20 datasheet for more information on the 12 bit temperature/data information construct.

The function readtemp12 does not work with the older DS1820 or DS18S20 as they have a different internal resolution. This command is not designed to be used with parasitically powered DS18B20 sensors, the 5V pin of the sensor must be connected.

Example:

    'Chip Settings. Assumes the development board with with a 16F877A
    #chip 16F877A,1

    #include <DS18B20.h>

    'Use LCD in 4 pin mode and define LCD pins
    #define LCD_IO 4
    #define LCD_RW PORTE.1
    #define LCD_RS PORTE.0
    #define LCD_Enable PORTE.2
    #define LCD_DB4 PORTD.4
    #define LCD_DB5 PORTD.5
    #define LCD_DB6 PORTD.6
    #define LCD_DB7 PORTD.7

; ----- DS18B20 port settings
    #define DQ PortC.3

; ----- Variables
    Dim TempC_100 as word   ' a variabler to handle the temperature calculations
    Dim CCOUNT, SIGNBIT, WHOLE, FRACT, DIG as Byte
    Dim TempC_100 as word   ' a variable to handle the temperature calculations

    ccount = 0
    CLS

    do forever

       'Display the integer and decimal value of the sensor on the LCD

       ' The function readtemp12 returns the raw value of the sensor.
       ' The sensor is read as a 12 bit value. Each unit equates to 0.0625 of a degree
       DSdata = readtemp12
       SignBit = DSdata / 256 / 128
       If SignBit = 0 Then goto Positive
       ' its negative!
       DSdata = ( DSdata # 0xffff ) + 1 ' take twos comp

    Positive:

       ' Convert value * 0.0625. Mulitple value by 6 then add result to multiplication of the value with 25 then divide result by 100.
       TempC_100 =  DSdata * 6
       DSdata = ( DSdata * 25 ) / 100
       TempC_100 = TempC_100 + DSdata

       Whole = TempC_100 / 100
       Fract = TempC_100 % 100
       If SignBit = 0 Then goto DisplayTemp
       Print "-"

    DisplayTemp:
       locate 1,0
       print hex(ccount)
       print " Real"
       locate 1,8
       print str(Whole)
       print "."
      ' To ensure the decimal part is two digits
       Dig = Fract / 10
       print Dig
       Dig = Fract % 10
       print Dig
       print chr(223)
       print "C"
       wait 2 s
       ccount++

    loop