'1WDS1820.BAS     29 March 2012
 'By Ian Delaney
 
 PinNbr = 42
 
 GetTemp PinNbr, Temp, pow$, dev$, code$
 Print "The temperature is:" format$(Temp,"% 1.3f"); " degrees C"
 print dev$;code$;pow$
 
 ''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
 ' Subroutine to get the temperature from a Dallas DS18B20/DS18S22
 '    or DSS20/DS1820 externally or parasite powered via 1-wire protocol.
 ' Reports temperature, device family, ROM Code and Power connection.
 ' Only 1 device allowed on the cable.
 '                                                 Iandaus
 ''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
 
Sub GetTemp (PinNbr, Value,pow$,dev$, code$)
 Local T1, T2, t, a1,a2,a3,a4,a5,a6,a7,a8, device, presence, power
 Local Countrem, T1C, TConv, T1t, T1t16, Value12, a,b,c,d,e,f,g,h
 
 Tconv=750    'max time mS for temp conversion in parasite mode
 ' for slowest device
 
 ''''''''''''''''''''''''''''''
 '   Check a device is present
 ''''''''''''''''''''''''''''''
 ONEWIRE RESET PinNbr
 presence  = mm.onewire            ' reset
 print "MM.ONEWIRE ";presence
 if presence = 0 then                  ' no device
   temp = 999.99
   dev$ = "No device found!"
   code$ = ""
   pow$ = ""
   exit sub
 endif
 
 ''''''''''''''''''''''''''''''''''''''''''''''
 '   check whether power external or parasitic
 ''''''''''''''''''''''''''''''''''''''''''''''
 ONEWIRE RESET PinNbr
 ONEWIRE Write PinNbr, 1,2,&hcc, &hb4
 ONEWIRE Read PinNbr,4,1,power
 if power = 1 then
   pow$ = " using External Power."
 else
   pow$ = " using Parasitic Power."
 endif
 
 ''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
 '   get ROM Code - useful if you want more than 1 device on wire
 ''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
 ONEWIRE Write PinNbr,1,1,&h33 'read ROM code
 ONEWIRE Read PinNbr,0,8,a1,a2,a3,a4,a5,a6,a7,a8
 code$ = " with ROM Code "+ hex$(a1,2)+" "+hex$(a2,2)+" "+hex$(a3,2)+" "+hex$(a4,2)+" "
 code$ = code$ + hex$(a5,2)+" "+hex$(a6,2)+" "+hex$(a7,2)+" "+hex$(a8,2)
 
 ''''''''''''''''''''''''''''''''''''''''''''''
 '   determine device family from code
 ''''''''''''''''''''''''''''''''''''''''''''''
 if a1=16 then
   dev$ = "on DS1820/DS18S20"
 elseif a1=34 then
   dev$ = "on DS18S22"
 elseif a1=40 then
   dev$ = "on DS18B20"
 else
   dev$ = "Not known"
 endif
 
 ''''''''''''''''''''''''''''''''''''''''''''''
 '   read temperature
 ''''''''''''''''''''''''''''''''''''''''''''''
 ONEWIRE reset PinNbr                        ' reset before command (or use flag=9)
 ONEWIRE Write PinNbr, 8, 2, &hcc, &h44      ' start conversion
 
 'read external when bit goes hi, for parasitic just wait
 If power = 0 Then
   Pause Tconv
 Else
   t = Timer
   Do
     If Timer - t > 1000 Then Error "Sensor not responding"
     Onewire Read PinNbr, 4 , 1 , b            ' conversion done?
   Loop Until b = 1
print "Conversion time: ";timer-t
 EndIf
 
 'read temperature from scratchpad and convert to degrees C + or -
 ONEWIRE Write PinNbr, 1, 2, &hcc, &hbe      ' command read data
 ONEWIRE Read PinNbr, 2, 2, T1, T2           ' get the data
 ONEWIRE Reset PinNbr
 
 ''''''''''''''''''''''''''''''''''''''''''''''
 '   calculate temp depending on device in use
 ''''''''''''''''''''''''''''''''''''''''''''''
 'Need to analyse type of chip to calculate temp from T1 and T2
 'T2 is MSB containing sign, T1 is LSB
 if a1=34 or a1=40 then          'DS18S22 or DS18B20 is 12 bit
   If T2 And &b1000 Then       'negative temp
     'make 2s complement (1s complement+1)
     T2 = (T2 xor &b11111111)
     T1 = (T1 xor &b11111111)+1
     if T1=1 then T2=T2+1        'add the carry if required
     Value = ((T2 And &b111) * 256 + T1) / 16
     Value = -Value
   else                            'positive temp
     Value = ((T2 And &b111) * 256 + T1) / 16
   endif
 elseif a1=16 then                   'DS18S20 or DS1820 is 9bit or calc to 12bit
   if T2 AND &b10000000 then       'if MSB of T2=1 then negative
     'Read 12bit resolution and adjust
     'read scratchpad using matchrom to get Count Remaining @byte 7
     ONEWIRE Write PinNbr,1,9,&h55,a1,a2,a3,a4,a5,a6,a7,a8  'read from scratchpad
     ONEWIRE Write PinNbr,0,1,&hbe
     ONEWIRE Read PinNbr,0,8,a,b,c,d,e,f,g,h
     COUNTREM=g
     'truncate 0.5deg value (or use integer division \)
     T1t = T1 AND &b11111110
     T1t=T1t / 2                   'make whole degrees
     'add compensation values read from scratchpad
     T1t16=T1t*16                  'make lsb 1/16 degree
     Value12 = T1t16 -4 +(16 - COUNTREM)    'add 12 bit value
     'take 2s complement
     T1C = (Value12 XOR &b11111111111) + 1
     Value = T1C/16                'make decimal value in degrees
     Value = -Value
   else                              'positive temp
     Value = T1 / 2                '9bit value
     'Read 12bit resolution and adjust
     'read scratchpad using matchrom
     ONEWIRE Write PinNbr,1,9,&h55,a1,a2,a3,a4,a5,a6,a7,a8  'read from scratchpad
     ONEWIRE Write PinNbr,0,1,&hbe
     ONEWIRE Read PinNbr,0,8,a,b,c,d,e,f,g,h
     COUNTREM=g
     T1t = T1 AND &b11111110      'truncate 0.5deg(or use integer division \)
     Value = T1t/2
     Value = Value - 0.25 + (16 - COUNTREM) /16   '12 bit value
   endif
 endif
End Sub

MM.ONEWIRE  1
The temperature is: 21.000 degrees C
on DS18B20 with ROM Code 28 CA A0 F2 05 00 00 3E using Parasitic Power.
>