readtemp

ReadTemp

Syntax:

    byte_var = ReadTemp

Command Availability:

Available on all microcontrollers.

Explanation:

ReadTemp 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

ReadTemp reads the sensor and stores in output variable. The conversion takes up to 750ms. Readtemp carries out a full 12 bit conversion and then rounds the result to the nearest full degree Celsius.

To read the full 12 bit value of the sensor use the readtemp12 command.

The temperature is read back in whole degree steps, and the sensor operates from -55 to + 125 degrees Celsius. Note that bit 7 is 0 for positive temperature values and 1 for negative values (ie negative values will appear as 128 + numeric value).

Note the Readtemp command 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

      ccount = 0
      CLS

    do forever
       ' The function readtemp returns the integer value of the sensor
       DSdata = readtemp

       ' Display the integer value of the sensor on the LCD
       locate 0,0
       print hex(ccount)
       print " Ceil"
       locate 0,8
       print DSdata
       print chr(223)+"C"

       wait 2 s
       ccount++

    loop