' Name        : TEMPX.pbp
' Compiler    : PICBASIC PRO Compiler 2.6
' Assembler   : PM or MPASM
' Target PIC  : 40-pin 16F877, 877A or similar
' Hardware    : LAB-X1 Experimenter Board
' Oscillator  : 4MHz external crystal
' 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

' 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 PORTC.0   ' Alias DS1820 data pin
DQ_DIR  Var TRISC.0   ' Alias DS1820 data direction pin

   ADCON1 = 7         ' 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
 @ nop                 ' Delay 1us at 4MHz
   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
 @ nop                 ' Delay 1us at 4MHz
   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