'1WDS1820.BAS 29 March 2012 'By Ian Delaney PinNbr = 20 GetTemp PinNbr, Temp, power$, device$, code$ Print "The temperature is:" format$(Temp,"% 1.3f"); " degrees C" print device$;code$;power$ '''''''''''''''''''''''''''''''''''''''''''''''''''''''''''' ' 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,power$,device$, code$) Local T1, T2, t, a1,a2,a3,a4,a5,a6,a7,a8, device, presence, power Local Countrem, T1C, TConv, T1t, T1t16, Value12, a,b,c,d,e,f,g,h Tconv=750 'max time mS for temp conversion in parasite mode ' for slowest device '''''''''''''''''''''''''''''' ' Check a device is present '''''''''''''''''''''''''''''' OWReset PinNbr,presence ' reset if presence = 0 then ' no device temp = 999.99 device$ = "No device found!" code$ = "" power$ = "" exit sub endif '''''''''''''''''''''''''''''''''''''''''''''' ' check whether power external or parasitic '''''''''''''''''''''''''''''''''''''''''''''' OWReset PinNbr,presence OWWrite PinNbr, 1,2,&hcc, &hb4 OWRead PinNbr,4,1,power if power = 1 then power$ = " using External Power." else power$ = " using Parasitic Power." endif '''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''' ' get ROM Code - useful if you want more than 1 device on wire '''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''' OWWrite PinNbr,1,1,&h33 'read ROM code OWRead PinNbr,0,8,a1,a2,a3,a4,a5,a6,a7,a8 code$ = " with ROM Code "+ str$(a1)+" "+str$(a2)+" "+str$(a3)+" "+str$(a4)+" " code$ = code$ + str$(a5)+" "+str$(a6)+" "+str$(a7)+" "+str$(a8) '''''''''''''''''''''''''''''''''''''''''''''' ' determine device family from code '''''''''''''''''''''''''''''''''''''''''''''' if a1=16 then device$ = "on DS1820/DS18S20" elseif a1=34 then device$ = "on DS18S22" elseif a1=40 then device$ = "on DS18B20" else device$ = "Not known" endif '''''''''''''''''''''''''''''''''''''''''''''' ' read temperature '''''''''''''''''''''''''''''''''''''''''''''' owreset PinNbr ' reset before command (or use flag=9) OWWrite 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" OWRead PinNbr, 4 , 1 , b ' conversion done? Loop Until b = 1 EndIf 'read temperature from scratchpad and convert to degrees C + or - OWWrite PinNbr, 1, 2, &hcc, &hbe ' command read data OWRead PinNbr, 2, 2, T1, T2 ' get the data OWReset 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 OWWrite PinNbr,1,9,&h55,a1,a2,a3,a4,a5,a6,a7,a8 'read from scratchpad OWWrite PinNbr,0,1,&hbe OWRead 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 OWWrite PinNbr,1,9,&h55,a1,a2,a3,a4,a5,a6,a7,a8 'read from scratchpad OWWrite PinNbr,0,1,&hbe OWRead 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