ds18s20 reads incorectly

[Bruce]

Your bit-banged read & write routines use a @ NOP for a 1uS delay, but you're running
at 20MHz so these are only 200nS. You would need 5 x @ NOP for a 1uS delay.

[jcleaver]

Thanks For The Math Help
As For As Speed Goes I Have Treid 4 And 20 Does Not Make A Difference

Will Work On The Math Issue

Do You Have The Thermostat Program In Pbp Not Hex

Thanks

[Acetronics2]

Hi, Jcleaver

The thermostat program was for you to verify what you had to find ... and show you a different Bargraph view.

NOT to copy / paste it ...

You can find any parts of it on this forum, The DS18x20 subject has been widely explored during the past months.

but that need some little efforts ... is it the problem ?

Alain

[skimask]

NOT to copy / paste it ...
...............................
but that need some little efforts ... is it the problem ?

Awwwww!!!!!

[CocaColaKid]

This code works great and gives the correct temperature throughout the sensors range in both Fahrenheit and Celsius. The format is like this: TempC = 2250 = 22.50ºC, TempF = 7250 = 72.50ºF.

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

[manwolf]

Jack

The reason your PBP version did not work was because:

You attempted to convert C to F using the RAW temp from the DS18S20.

TEMP = ((TEMP*9/5)+32 )

Then tried to calculate the temp from the results.

Lcdout $fe, 1, dec (temp >> 1),".",dec(temp.0 * 5)," degrees C"

For the fun of it lets plug some numbers in assume 27.5 C is the temp today.

From the datasheet : The temperature sensor output has 9-bit resolution, which corresponds to 0.5°C steps.

so 27.5*2 = 55

Temp = (55*9/5) + 32 = 131
So Temp now is equal to 131.

Next we shift right 131>>1 same as temp/2 = 65.5

Hmmm 65.535 does that number ring a bell?

Wonder what would happen if you were to shift first then convert C to F like all of the other code posted does?

temp = (temp>>1*9/5) +32 = (27.5*9/5)+32 = 81.5 F

Hopefully this explains to you why it works in MikroBasic and not in PBP. The math is not broken, just the order of operation.

That is why I said check math, simple change would fix it.

Acetronic: I ask because you posted for jcleaver, would not take without asking first.

[skimask]

You attempted to convert C to F using the RAW temp from the DS18S20.
TEMP = ((TEMP*9/5)+32 )
Then tried to calculate the temp from the results.
Lcdout $fe, 1, dec (temp >> 1),".",dec(temp.0 * 5)," degrees C"

Nice find. I should've caught that the first time around.

[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.