Math for dunce...

[fratello]

I have three value : 25 ; 25.23 ; 26.02
I must do this : If 26.02 - (25/100) > 25.23 then do something...
Since the numbers are not integers, my results are wrongs. Please, a little help. Thanks in advance.

[Darrel Taylor]

Just multiply everything by 100.
Then it becomes ...

If (2602 - 25) > 2523 then do something...
<br>

[fratello]

Thank You, Mr.Darrel !
I have already do this, but...Maybe it's another mistake..So, I put the code.
I read the temperature :

 OWOut DQ, 1, [$CC, $44] 
 OWOut DQ, 1, [$CC, $BE]
 OWIn DQ, 2, [temperature.byte0, temperature.byte1]         
                SignBit = 0
                if  temperature.15 then  
                    temperature  = ~ temperature + 1 
                    SignBit = 1 
                endif  
                
Dummy = 625 * Temperature
TempC = DIV32 10
TempC = (Temperature & $7FF) >> 4
Float = ((Temperature.Lowbyte & $0F ) * 25 )>>2
Temperature=TempC*100 + Float         
 	If SignBit then
  		V= 10000 - Temperature   	' 25'C=12500  0'C=10000  -10'C=9000 
  		SignBit = 0
 	   else
  		V= 10000 + Temperature
 	EndIf
 
	If V >= 10000 then             	' Above 0 C.      
  		Temperature=V-10000                   
 	   else                                   
  		Temperature=10000-V      	' Below 0 C. 
 	EndIf
 
 GoSub SelectSign                    	' +/blank/- Sign

SelectSign:
 If v = 10000 then                      	' Temperature = 0 C.
  	Sign=" " 				      ' No sign
     Else 
  		If v < 10000 then             ' <> 0
   			Sign="-"			' Temperature below 0 C.	
  		    Else
   			Sign="+"			' Temperature above 0 C.
  		EndIf
 EndIf
Return

At the beginning I set the hysterezis for thermostat :

 If Mode=1 then                        	' Set Hysteresis  
                LcdReg  =  %10000000 + 12 ' cursor  X
                call    PrintCtrlLcd
                LcdReg  =  %01000010      ' cursor  Y
                call    PrintCtrlLcd          
                Char = 21
                call    PrintChar 
                Char = 19
                call    PrintChar  
                Char = 20
                call    PrintChar  
                Char = 15
                call    PrintChar  
  Gosub DTemp                           	' Display Hysteresis
  If (PORTB.1=0) Or (PORTB.2=0) then    	' Up or down button pushed  

   If PORTB.2=0 then                    	' Down button
            if hyst > 5 then hyst=hyst-5
            If Hyst < 5  then Hyst=5
            Gosub Debounce
   EndIf
   If PORTB.1=0 then                    	' Up button
            hyst=hyst+5
            If Hyst > 50 then Hyst=50
            Gosub Debounce
   EndIf 
   Gosub DTemp                            ' Display Hysteresis                        
  EndIf
 EndIf
.....
DTemp :
         LcdReg  =  %10100000 + 14      	' cursor  X  
         call    PrintCtrlLcd
         LcdReg  =  %01000100           	' cursor  Y
         call    PrintCtrlLcd        
   
         Char = (hyst dig 2) + 2            
         call    PrintChar
         Char = 14                       
         call    PrintChar
         Char = (hyst dig 1) + 2           
         call    PrintChar
         Char = (hyst DIG 0) + 2      
         Call    PrintChar
Return

and I try to do this :

check:
 if temperature > (tref + hyst) then
    tref=temperature
 		duratavar=(temperature-tref)/hyst
 		duratavar=duratavar*durata
 	if tipsun=2 then
 		sound PORTB.6, [varsnd, duratavar] 
     	    else
 		sound PORTB.6, [varsnd, 20]                           
 	endIf
 endif

 if temperature < (tref - hyst) then
    tref=temperature
 		duratavar=(tref-temperature)/hyst
 		duratavar=duratavar*durata
 	if tipsun=2 then
 		sound PORTB.6, [varsnd2, duratavar]
 	    else
 	      sound portb.6, [varsnd2, 10]
 	endif
 endif
Return

Everything works great, but this "if temperature > (tref + hyst) then" return wrong results.
Note : hyst, temperature, tref are var Word.
Hysterezis must be max 0.50 'C, with step of 0.05 'C. On display works fine, but inside the code I think I made mistake...Thank You !

[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 !