See comments in code

> -----Original Message-----
> From: Francois Robbertze [SMTP:fr10@PIXIE.CO.ZA]
> Sent: Friday, January 05, 2001 9:45 AM
> To:   PICLIST@MITVMA.MIT.EDU
> Subject:      [PIC]: Thermostat Routine?
>
> Dear Piclist Members
>
> The routine read the temperature from a Dallas1820
> UpperT = 27 deg C (54)
> LowerT = 23 deg C (46)
> Element is a Triac
>
> As the temperature rises with the Element on it will switch off at 27 deg
> C which is OK.
> As the temperature now decreases the Element should switch on below the
> LowerT value, but it don't - It switch on at a value below 27 deg again???
>
> Can someone tell me where am I going wrong...
>
> Main
> call Thermostat
>
> Thermostat
>  call ReadTemp         ; Subroutine to read temperature from Dallas1820
>  movlw 'E'                  ;Test for failure in dallas1820
>  subwf Temp,W
>  btfsc STATUS,Z
>  goto DallasError
>
>  movfw Temp
>  subwf UpperT,W
        ; Subtract the current temperature from UpperT
        ; if current temperature is higher than UpperT, the result
        ; will be negative and Carry will be set
>  btfss STATUS,C
        ; this should be btfsc STATUS,C
>  call HeatingOff
>
>  movfw Temp
>  subwf LowerT,W
        ; Subtract current temperature from LowerT
        ; If current temperature is lower than LowerT, the result
        ; will be positive and Carry will be clear
>  btfsc STATUS,C
        ; this should be btfss STATUS,C
>  call HeatingOn
>  return
>
> HeatingOn
>  bsf Element
>  return
>
> HeatingOff
>  bcf Element
>  return
>
> DallasError
>  bcf Element     ; do no heating and
>  return              ;return to main loop
>
>

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