ds18s20 reads incorectly

[ecoli-557]

I am trying to follow your code in an effort to better understand it, but I don't understand
SignC = Positive

ReadDS18S20:
    owout sensor,1,[$CC, $44]                       ' Send Start Temperature Conversion command
    owout sensor,1,[$CC, $BE]                       ' Send Read Temperature command
    owin sensor,0,[STR dq\9]                        ' Retrieve all 9 bytes of data
    RawTemp.Byte0 = dq[0]
    RawTemp.byte1 = dq[1]
    if RawTemp.8 = 1 then                           ' Check if temperature is a negative reading
        SignC = Negative
        RawTemp.lowbyte = RawTemp.lowbyte ^ 255     ' Invert data
        else
        SignC = Positive
	endif
    dummy = RawTemp.0                               ' Store the half degree indicator bit
    TempC = ((RawTemp.lowbyte) >> 1) * 100          ' Divide raw data by 2 to give real temperature
    TempC = TempC + (dummy * 50)                    ' Add the half degree is present
    if SignC = Negative then                        ' Only proceed if temperature is negative
        if TempC => 1770 then   
            SignF = Negative
            TempF = (TempC + 5000) * 900
            TempF = div32 500
            TempF = TempF - 12200
            return 
            else
            SignF = Positive
            TempF = (TempC + 5000) * 900
            TempF = div32 500
            TempF = 12200 - TempF
            return 
        endif    
    endif
    SignF = Positive
    TempF = TempC * 18 / 10 + 3200
return

It would help if you shared the declarations of the variables used.
sensor equates to the hardware pin connected to the sensor?
RawTemp is a word?
dq is an array of 9?
dummy is a byte?
TempC is a byte?
TempF is a byte?

I don't get SignC or SignF and how you can equate to 'Positive' or 'Negative', I couldn't find a reference in the PBP manual.
Explanation would be appreciated.
Regards,
Steve

[EarlyBird2]

I don't get SignC or SignF and how you can equate to 'Positive' or 'Negative', I couldn't find a reference in the PBP manual.
Explanation would be appreciated

For positive temperatures the output increases from 0000h as the temperature increases from 0 deg C.
For negative temperatures the output decreases from FFFFh as the temperature falls below -0.5 deg C.

To check for negative any output bit can be checked for 1, when that bit is outside the temperature range of the sensor. The data sheet says

The sign bit (S) indicates if the value is positive or negative: for positive numbers S = 0 and for negative numbers S = 1.

In the program RawTemp.8 is chosen as the sign bit.

[ecoli-557]

Thanks EarlyBird2, I did figure that part out. In the code that the 'Kid' supplied, I could not get it to work until I remarked the SignC=Negative portion.
The code below works, but I have not tried for negative numbers yet..... Could you explain why?
Thanks and Regards,
Steve

ReadDS18S20:' Works, mostly.....------------------------------------------------
                  owout Tsensor,1,[$CC, $44]                                    'Send Start Temperature Conversion command
                  owout Tsensor,1,[$CC, $BE]                                    'Send Read Temperature command
                  owin Tsensor,0,[STR dq\9]                                     'Retrieve all 9 bytes of data
                  RawTemp.Byte0 = dq[0]
                  RawTemp.byte1 = dq[1]
                  if RawTemp.8 = 1 then                                         'Check if temperature is a negative reading
                     SignC = Negative                                            
                     RawTemp.lowbyte = RawTemp.lowbyte ^ 255                    'Invert data
                  else
                     SignC = Positive
                  endif
                  dummy = RawTemp.0                                             'Store the half degree indicator bit
                  TempC = ((RawTemp.lowbyte) >> 1) * 100                        'Divide raw data by 2 to give real temperature
                  TempC = TempC + (dummy * 50)                                  'Add the half degree is present
'                 if SignC = Negative then                                      'Only proceed if temperature is negative - doesnt work for F, fine for C
'                    if TempC => 1770 then   
'                       SignF = Negative
'                       TempF = (TempC + 5000) * 900
'                       TempF = div32 500
'                       TempF = TempF - 12200
'                    return 
'                  else
'                      SignF = Positive
'                      TempF = (TempC + 5000) * 900
'                      TempF = div32 500
'                      TempF = 12200 - TempF
'                      return 
'                   endif    
'                 endif
                  SignF = Positive                                              'Sign is +
                  TempF = ((TempC * 18) / 10) + 3200                            'Convert from C to F
                  return

[EarlyBird2]

Negative and Positive are declared variables or constants. In your code should be

Negative CON 1
Positive CON 0

Does this help?

Could be SYMBOL or ALIAS of course.

[ecoli-557]

EarlyBird2-
Thanks! I just tried it (I did NOT have them as CONstants), compiles fine but still gives me 0.00F.
Code is below for clarification.
Regards,
Steve

    Positive    con 0                                                           'Bit used for + in the DS18S20
    Negative    con 1                                                           'Bit used for - in the DS18S20
    rawtemp         var word                                                    'Raw temp var
    tempC           var word                                                    'Temp var for degrees C
    tempF           var word                                                    'Temp var for degrees F
    dq              var byte[9]                                                 'String of data from DS18S20
    SignC           var bit                                                     'Bit for + or - for degrees C
    SignF           var bit                                                     'Bit for + or - for degrees F
    dummy           var bit                                                     'Temp var

ReadDS18S20:' Works, mostly.....--Thanks 'Kid' from Forum-----------------------
                  owout Tsensor,1,[$CC, $44]                                    'Send Start Temperature Conversion command
                  owout Tsensor,1,[$CC, $BE]                                    'Send Read Temperature command
                  owin Tsensor,0,[STR dq\9]                                     'Retrieve all 9 bytes of data
                  RawTemp.Byte0 = dq[0]
                  RawTemp.byte1 = dq[1]
                  if RawTemp.8 = 1 then                                         'Check if temperature is a negative reading
                     SignC = Negative                                            
                     RawTemp.lowbyte = RawTemp.lowbyte ^ 255                    'Invert data
                  else
                     SignC = Positive
                  endif
                  dummy = RawTemp.0                                             'Store the half degree indicator bit
                  TempC = ((RawTemp.lowbyte) >> 1) * 100                        'Divide raw data by 2 to give real temperature
                  TempC = TempC + (dummy * 50)                                  'Add the half degree is present
                 if SignC = Negative then                                      'Only proceed if temperature is negative - doesnt work for F, fine for C
                    if TempC => 1770 then   
                       SignF = Negative
                       TempF = (TempC + 5000) * 900
                       TempF = div32 500
                       TempF = TempF - 12200
                    return 
                  else
                      SignF = Positive
                      TempF = (TempC + 5000) * 900
                      TempF = div32 500
                      TempF = 12200 - TempF
                      return 
                   endif    
                 endif
'                  SignF = Positive                                              'Sign is +
'                  TempF = ((TempC * 18) / 10) + 3200                            'Convert from C to F
                  return

This what I have that does work, just not for negatives.....

ReadDS18S20:' Works, mostly.....--Thanks 'Kid' from Forum-----------------------
                  owout Tsensor,1,[$CC, $44]                                    'Send Start Temperature Conversion command
                  owout Tsensor,1,[$CC, $BE]                                    'Send Read Temperature command
                  owin Tsensor,0,[STR dq\9]                                     'Retrieve all 9 bytes of data
                  RawTemp.Byte0 = dq[0]
                  RawTemp.byte1 = dq[1]
                  if RawTemp.8 = 1 then                                         'Check if temperature is a negative reading
                     SignC = Negative                                            
                     RawTemp.lowbyte = RawTemp.lowbyte ^ 255                    'Invert data
                  else
                     SignC = Positive
                  endif
                  dummy = RawTemp.0                                             'Store the half degree indicator bit
                  TempC = ((RawTemp.lowbyte) >> 1) * 100                        'Divide raw data by 2 to give real temperature
                  TempC = TempC + (dummy * 50)                                  'Add the half degree is present
'                 if SignC = Negative then                                      'Only proceed if temperature is negative - doesnt work for F, fine for C
'                    if TempC => 1770 then   
'                       SignF = Negative
'                       TempF = (TempC + 5000) * 900
'                       TempF = div32 500
'                       TempF = TempF - 12200
'                    return 
'                  else
'                      SignF = Positive
'                      TempF = (TempC + 5000) * 900
'                      TempF = div32 500
'                      TempF = 12200 - TempF
'                      return 
'                   endif    
'                 endif
                  SignF = Positive                                              'Sign is +
                  TempF = ((TempC * 18) / 10) + 3200                            'Convert from C to F
                  return

Regards,
Steve

[EarlyBird2]

these two lines are commented out?

' SignF = Positive 'Sign is +
' TempF = ((TempC * 18) / 10) + 3200 'Convert from C to F

so I guess you will get 0 deg F

[ecoli-557]

Steve-
Dunno what I had thought I was looking at, but when I un-commented those other lines, I now get correct readings!
This is now what seems to be working:
BTW, going to be in your neck of the woods this Wednesday, 2 days in London, then take a boat out from South Hampton on a cruise through the Baltics.
Thanks for pushing me in the right track!
Regards,
Steve

ReadDS18S20:' Works, Thanks 'Kid' and Steve from the UK....from Forum-----------
                  owout Tsensor,1,[$CC, $44]                                    'Send Start Temperature Conversion command
                  owout Tsensor,1,[$CC, $BE]                                    'Send Read Temperature command
                  owin Tsensor,0,[STR dq\9]                                     'Retrieve all 9 bytes of data
                  RawTemp.Byte0 = dq[0]
                  RawTemp.byte1 = dq[1]
                  if RawTemp.8 = 1 then                                         'Check if temperature is a negative reading
                     SignC = Negative                                            
                     RawTemp.lowbyte = RawTemp.lowbyte ^ 255                    'Invert data
                  else
                     SignC = Positive
                  endif
                  dummy = RawTemp.0                                             'Store the half degree indicator bit
                  TempC = ((RawTemp.lowbyte) >> 1) * 100                        'Divide raw data by 2 to give real temperature
                  TempC = TempC + (dummy * 50)                                  'Add the half degree is present
                 if SignC = Negative then                                      'Only proceed if temperature is negative - doesnt work for F, fine for C
                    if TempC => 1770 then   
                       SignF = Negative
                       TempF = (TempC + 5000) * 900
                       TempF = div32 500
                       TempF = TempF - 12200
                    return 
                  else
                      SignF = Positive
                      TempF = (TempC + 5000) * 900
                      TempF = div32 500
                      TempF = 12200 - TempF
                      return 
                   endif    
                 endif
                  SignF = Positive                                              'Sign is +
                  TempF = ((TempC * 18) / 10) + 3200                            'Convert from C to F
                  return