; Chapter 12 6812 assembly language programs
; Jonathan W. Valvano, 2/26/07
; This software accompanies the book,
; Embedded Microcomputer Systems: Real Time Interfacing, Second Edition
; published by Thomson Engineering, 2006



        xref ADCtable  ; monotonic list of ADC values
        xref Ttable    ; list of corresponding temperature values 
        absentry LookUp 
;**********Lookup*******************
;Inputs: RegD is 0 to 65534 Xdata point, xL
;     RegD input must be greater than or equal to first Xdata point
;     RegD input must be less than last Xdata point
;Output: RegD is 0 to 65535 Ydata point, decimal fixed-point 0.1C    
;Registers destroyed: X,Y,B,CCR
LookUp: ldx  #ADCtable  ; first find x1<=xL<x2
        ldy  #Ttable  
search  cpd  2,x      ; check xL<x2
        blo  found    ; stops when X points to x1
        leax 2,x
        leay 2,y
        bra  search
found   subd 0,x      ; xL-x1
        pshd
        ldd  2,x      ; x2
        subd 0,x      ; D=x2-x1
        tfr  D,X      ; X=x2-x1
        puld          ; D=(xL-x1) 
        fdiv          ; X=(65536*(xL-x1))/(x2-x1)
        tfr  X,D
        tfr  A,B      ; B=(256*(xL-x1))/(x2-x1)  
        etbl 0,y	    ; Y=>y1,y2
        rts	          ; D=Y1+B*(Y2-Y1)
;Program 12.1.  Assembly language program to convert 8-bit ADC into fixed-point temperature.