ME Labs, Inc. | 1-719-520-5323 | Example Program - TEMPXU.pbp

' Name        : TEMPXU.pbp
' Compiler    : PICBASIC PRO Compiler 2.6
' Assembler   : MPASM
' Target PIC  : PIC18F4550 or similar type
' Hardware    : LAB-XUSB Experimenter Board
' Oscillator  : 20MHz external
' Keywords    : LCDOUT
' Description : PICBASIC PRO program to read DS1820 1-wire
' temperature sensor and display temperature on LCD.
'

' Define LOADER_USED to allow use of the boot loader.
' This will not affect normal program operation.
Define LOADER_USED 1

' RESET_ORG can be set to move the BASIC program out of the way
' of any boot loader running from location 0, such as the
' Microchip USB boot loader
'Define RESET_ORG 800h

Define OSC 48      ' Core is running at 48MHz

' Define LCD pins
Define LCD_DREG  PORTD
Define LCD_DBIT  4
Define LCD_RSREG PORTE
Define LCD_RSBIT 0
Define LCD_EREG  PORTE
Define LCD_EBIT  1

' Allocate variables
command Var Byte       ' Storage for command
i       Var Byte       ' Storage for loop counter
temp    Var Word       ' Storage for temperature
DQ      Var PORTA.2    ' Alias DS1820 data pin
DQ_DIR  Var TRISA.2    ' Alias DS1820 data direction pin

   ADCON1 = 15         ' Set PORTA and PORTE to digital
   Low PORTE.2         ' LCD R/W line low (W)
   Pause 100           ' Wait for LCD to start
   Lcdout $fe, 1, "Temp in degrees C" ' Display sign-on message

' Mainloop to read the temperature and display on LCD
mainloop:
   Gosub init1820       ' Init the DS1820
   command = $cc        ' Issue Skip ROM command
   Gosub write1820

   command = $44        ' Start temperature conversion
   Gosub write1820
   Pause 2000           ' Wait 2 seconds for conversion to complete
   Gosub init1820       ' Do another init

   command = $cc        ' Issue Skip ROM command
   Gosub write1820
   command = $be        ' Read the temperature
   Gosub write1820
   Gosub read1820

   ' Display the decimal temperature
   Lcdout $fe, 1, dec (temp >> 1), ".", dec (temp.0 * 5), " degrees C"
   Goto mainloop        ' Do it forever

' Initialize DS1820 and check for presence
init1820:
   Low DQ               ' Set the data pin low to init
   Pauseus 500          ' Wait > 480us
   DQ_DIR = 1           ' Release data pin (set to input for high)
   Pauseus 100          ' Wait > 60us
   If DQ = 1 Then
      Lcdout $fe, 1, "DS1820 not present"
      Pause 500
      Goto mainloop     ' Try again
   Endif
   Pauseus 400          ' Wait for end of presence pulse
   Return

' Write "command" byte to the DS1820
write1820:
   For i = 1 to 8       ' 8 bits to a byte
     If command.0 = 0 Then
        Gosub write0    ' Write a 0 bit
     Else
        Gosub write1    ' Write a 1 bit
     Endif
     command = command >> 1  ' Shift to next bit
   Next i
   Return

' Write a 0 bit to the DS1820
write0:
   Low DQ
   Pauseus 60              ' Low for > 60us for 0
   DQ_DIR = 1              ' Release data pin (set to input for high)
   Return

' Write a 1 bit to the DS1820
write1:
   Low DQ                  ' Low for < 15us for 1
   Pauseus 1               ' Delay 1us
   DQ_DIR = 1              ' Release data pin (set to input for high)
   Pauseus 60              ' Use up rest of time slot
   Return

' Read temperature from the DS1820
read1820:
   For i = 1 to 16         ' 16 bits to a word
     temp = temp >> 1      ' Shift down bits
     Gosub readbit         ' Get the bit to the top of temp
   Next i
   Return

' Read a bit from the DS1820
readbit:
   temp.15 = 1             ' Preset read bit to 1
   Low DQ                  ' Start the time slot
   Pauseus 1               ' Delay 1us
   DQ_DIR = 1              ' Release data pin (set to input for high)
   If DQ = 0 Then 
      temp.15 = 0          ' Set bit to 0
   Endif
   Pauseus 60              ' Wait out rest of time slot
   Return

   End

           

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