'TEMPALL.BAS March 2012

PinNbr = 20

GetTemp PinNbr, Temp, power$, device$, code$
Print "The temperature is:" format$(Temp,"% 1.2f"); " degrees C"
print device$;code$;power$

''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
' Subroutine to get the temperature from a Dallas DS18B20/DS18S22
' or DSS20/DS1820 externally or parasite powered.
' Reports temperature, device family, ROM Code and Power connection.
' Only 1 device allowed on the cable.
''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''

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, a,b,c,d,e,f,g,h

Tconv=750 'max time mS for temp conversion in parasite mode

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 ext/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
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
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

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

'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
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
T1C = T1 AND &b11111110 'truncate 0.5deg
Value = t1C/2
Value = Value - 0.25 + (16 - COUNTREM) /16 '12 bit value
endif
endif
End Sub