microlab experiment 3

microlab_exp_3.asm

      .org  4000
      LDS   #$5F00    
      LDAA  #$9       ; i value
      PSHA            ; send param
      JSR   FIB       ; sub routine result is in B reg
      PULA            ; get param
      SWI
FIB   TSX
      LDAA  2,x       ; get param
      CMPA  #$1       ; check if <= 1
      BLE   RES
      SUBA  #$2       ; call fib(n-2)
      PSHA            ; send param
      JSR   FIB       ; sub routine result is in B register
      PULA            ; get param
      TSX
      LDAA  2,x       ; get param
      PSHB            ; save previous result
      SUBA  #$1       ; call fib(n-1)
      PSHA            ; send param
      JSR   FIB       ; sub routine result is in B reg
      PULA            ; get param
      ABA             ; addition fib(n-2) + fib(n-1) (A <- A + B)
      TAB             ; store result in B reg
      RTS             ; return
RES   TAB             ; n (B <- A)
      RTS             ; return n