;combi.asm
.include "1200def.inc"

.def A=r16
.def Abar=r17
.def B=r18
.def Bbar=r19
.def C=r20
.def Dbar=r21
.def temp=r22

.cseg
.org 0
	rjmp RESET	;reset handle

RESET:      ldi temp, 0b00001111;
            out DDRB, temp      ;PB0-3 are inputs
                                ;PB4-7 are outputs

loop_here:  in temp, PINB       ;read PORTB pins
            mov A, temp
            mov Abar, temp
            com Abar            ;invert A
            mov B, temp
            mov Bbar, temp
            com Bbar            ;invert B
            mov C, temp
            mov Dbar, temp
            com Dbar            ;invert D
            andi A, 1           ;isolate the bit for A
            andi Abar, 1        ;isolate the bit for Abar
            lsr B               ;get input B to position bit0
            lsr Bbar

            lsr C               ;get input C to position bit0
            lsr C

            lsr Dbar            ;get input D to position bit0
            lsr Dbar
            lsr Dbar

            andi B, 1
            andi Bbar, 1
            andi C, 1
            andi Dbar, 1
            
            and A, Bbar         ;A = A * Bbar
            and B, Abar         ;B = Abar * B
            and C, Dbar         ;C = C * Dbar
            
            or A, B             ;A = (A * Bbar) + (Abar * B) 
            and A, C  ;A = ((A * Bbar) + (Abar * B))* (C  * Dbar) 

            and A, 1
            cpi A, 1
            breq Its1
            cbi PORTB, 4 ;no its 0, so reset PB4
            rjmp loop_here
Its1:       sbi PORTB, 4
            rjmp loop_here