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; Microcontroller Makes Linear Temperature Measurement Simple
; Author: Bonifacio Martin-del-Brio & Nicolas Medrano-Marques
;          Dept. Ingenieria Electronica y Comunicaciones
;          Universidad de Zaragoza, Zaragoza, Spain;
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; A/D and voltage-to-temperature conversion routine
; written for 68HC11
; Result: temperature in deg C in accumulator B
; -----------------------------------------------------------------------
; A/D conversion (the A/D must be enabled in RESET routine)
       LDAA      #1      ; single channel conversion (PE1 pin)
       STAA      $1030   ; ADCTL register, starts conversion
loopl  LDAA      $1030   ;
       BPL       loop1   ; A/D complete when ADCTL[7]=1
       LDAA      $1031   ; digital (hex) value of the input voltage

; Voltage to temperature (?C) conversion (in B accumulator)
       LDAB      #17      ;
       MUL                ; AxB=>D (17 x hex); 8x8 => 16-bits 
       LDX       #50      ;
       IDIV               ; D/X, quotient in X, remainder in D
                          ; (21 x hex /50)
       XGDX               ; X<=>D, value in B register
       SUBB      #18      ; temperature in B register
                          ; (17 x hex/50-18)
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