Math for dunce...

[Darrel Taylor]

Not really sure what all is going on in your program fratello.
So let me just show what I would do.

First ... It takes 750mS from the time you start a conversion till you can read the results.
You can just put a pause after the Convert command [$CC, $44], to wait till it's done.
Or you can Poll the DS18B20's busy bit.

Once you have the reading from the DS18B20, it can be converted like this...

    Sign = TempC.15
    TempC = ABS(TempC)
    TempC = ((TempC >> 4)*100) + ((TempC & $F)*100 >> 4)
    IF Sign THEN TempC = -TempC

That gives you a Signed Word with 2 decimal places.
25.00 °C would have the value 2500.
-10.00 °C would be -1000.
It will work with the full temperature range of the sensor -55°C to +125°C.

You can display it on an LCD with this ...

DisplayTemp:
    IF TempC.15 THEN LCDOUT "-"
    LCDOUT DEC ABS TempC/100,".", DEC2 ABS TempC,13,10
RETURN

To compare the Temp with your hysteresis range, you just subtract the values.
If the value being subtracted is larger than the other one, the result will be negative.
So, just testing for the sign bit tells you if it's above or below the setpoints.

Compare:
    Diff = (tref + Hyst) - TempC
    Over = Diff.15

    Diff = TempC - (tref - Hyst)
    Under = Diff.15
RETURN

Over and Under are BIT vars, so you can test them later in the program to activate alarms or whatever.

Keep in mind that with 12-bit resolution, each step of the DS18B20's reading is 0.0625°C.
So incrementing the hyst. 0.05°C won't always give the expected Hyst. range.
It'll be close, but not perfect.

Test program attached.

[fratello]

As always, Mr.Darrel it's one fine Gentleman. Thank You ! I will test and I will post the results !

[fratello]

It's OK, of course !
BTW: Just for fun ; I redefine in my source "hyst" as byte (previous = word) and the results are similares !