Using PLP tool: Your program should start by loading the numbers 2015 and 250 in

Question

Using PLP tool: Your program should start by loading the numbers 2015 and 250 into registers $a0 and $a1 respectively. The start of your program is a good place to initialize any other registers with values that you don’t plan on changing inside the program. It should then have an infinite loop that performs two steps: reading the value of the switches and use control flow instructions to perform the indicated arithmetic operation. The result should be stored in register $v0. After doing this it should return to the start of the loop and repeat these two steps. If an undefined switch value is read (i.e. it is not one of the switch values given below), $v0 should contain 0. Use the following switch convention Switch Number Hexadecimal Switch Value Binary Switch Value Operation Result ($v0) 0 0x00000001 0b00000001 $v0 = $a0 + $a1 2265 1 0x00000002 0b00000010 $v0 = $a0 - $a1 1765 2 0x00000004 0b00000100 $v0 = $a0 * $a1 503750 3 0x00000008 0b00001000 $v0 = $a0 AND $a1 218 4 0x00000010 0b00010000 $v0 = $a0 OR $a1 2047 this program has to be written using assembly language

Explanation / Answer

Below written assembly program code is another way to make a simple calculator:

model small
.stack ; Stack memory space for program instructions

.data

   ; Some messages to the user
   msgA DB "Enter the first one digit number: $"
   msgB DB 10, 13, "Enter the second one digit number: $"
   msgC DB 10, 13, "Enter which operator must be used: $"
   msgD DB 10, 13, 10, 13, "The answer is: $"
   msgE DB 10, 13, 10, 13, "!! Incorrect input, please retry !!", 10, 13, 10, 13, "$"

.code
  
   ; Skip variable declaration
   jmp start

   ; Define some variables
   charA DB ?
   charB DB ?
   result DB ?
   operator DB ?
  
   fail:
          
       ; Wrong input
       mov ah, 09
       mov dx, offset msgE
       int 21h
  
   start:
  
       ; Put the address of data into ax, ds
       mov ax, @data
       mov ds, ax
      
       ; Ask the user for the first single digit number
       mov ah, 09
       mov dx, offset msgA
       int 21h
      
       ; Use subfunction one to get character from keyboard
       mov ah, 01
       int 21h
       mov charA, al
      
       ; Jump if it's less than zero
       cmp charA, "0"
       jl fail
      
       ; Jump if greater than nine
       cmp charA, "9"
       jg fail
      
       ; Ask for second one digit number
       mov ah, 09
       mov dx, offset msgB
       int 21h
      
       ; Get input from keyboard for second number
       mov ah, 01
       int 21h
       mov charB, al
      
       ; Jump if it's less than zero
       cmp charB, "0"
       jl fail
      
       ; Jump if greater than nine
       cmp charB, "9"
       jg fail
      
       ; Ask for the operator
       mov ah, 09
       mov dx, offset msgC
       int 21h
      
       ; Store the operator in a variable
       mov ah, 01
       int 21h
       mov operator, al
      
       ; If operator is a plus go to addition
       cmp operator, "+"
       je addition
      
       ; But if it is a minus go to subtraction
       cmp operator, "-"
       je subtraction
      
       ; If it is neither then jump to fail
       jmp fail
      
   addition:
      
       ; Add charB to charA and store in ah
       mov ah, charA
       add ah, charB
      
       ; Move ah into result and convert to integer
       mov result, ah
       sub result, 48
      
       ; Jump to extra if the result is >9
       cmp result, 58
       jnb extra
      
       ; Show message
       mov ah, 09
       mov dx, offset msgD
       int 21h
      
       ; Print the result
       mov ah, 02
       mov dl, result
       int 21h
      
       ; Jump to exit
       jmp exit
      
   extra:
  
       ; Show message "The answer is"
       mov ah, 09
       mov dx, offset msgD
       int 21h
      
       ; Load "1" into ah (two single didgit numbers can
       ; Never be > 18. Therefore we know that if the result
       ; Is two digits, the first digit must be a "1"
       mov ah, 02
       mov dl, 49
       int 21h
      
       ; Find the unit component of the result and print
       sub result, 10
       mov ah, 02
       mov dl, result
       int 21h
      
       ; Jump to exit
       jmp exit
      
   subtraction:
  
       ; Jump to negative if charA is below charB
       mov ah, charA
       cmp ah, charB
       jb negative
      
       ; Subtract charB from charA
       mov ah, charA
       sub ah, charB
      
       ; Put ah into result and convert to decimal
       mov result, ah
       add result, 48
      
       ; Show message "The answer is"
       mov ah, 09
       mov dx, offset msgD
       int 21h
      
       ; Display result
       mov ah, 02
       mov dl, result
       int 21h
      
       ; Jump to exit
       jmp exit
      
   negative:
  
       ; Subtract charA from charB
       mov ah, charB
       sub ah, charA
       mov result, ah
       add result, 48
      
       ; Display message "The answer is"
       mov ah, 09
       mov dx, offset msgD
       int 21h
      
       ; Print out the negative sign
       mov ah, 02
       mov dl, 45
       int 21h
      
       ; Display the result
       mov ah, 02
       mov dl, result
       int 21h
      
   exit:
  
       ; Back to system - End program
       mov ax, 4c00h
       int 21h

; Indicate that no more commands follow
END

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