Convert Character to binary assembly language

Question

Hi i m using dosbox and masm compilor. I want to prompts the user to enter a character, and prints the ASCII code of the character in hex and in binary on the next line. Rep

Answer 1

When you have the value in register, it is stored in CPU in bits (0/1 encoded as low/high current voltage), so it's actually "formatted" in binary!

You just need to output eight characters '0'/'1' per bit, starting from most significant one.

At the moment where you have the character in AL, the code to output the binary form may look like this:

    cx = 8   ; 8 bits to output
bin_loop:
    rcl al,1 ; move most significant bit into CF
    setc bl  ; bl = 0 or 1 by CF (80386 instruction)
    add bl,'0' ; turn that 0/1 into '0'/'1' ASCII char
    call display_bl ; must preserve al and cx
    loop bin_loop

Judging by your usage of cx for loop you are in 16b real mode. So if you also can't use 80386 instructions (setc) (when targetting 8086/80186/80286 CPU, like emu8086 emulator), then this can be achieved in other way (like two instructions for example, instead of one).

From your usage of CF in those loops with shl/rcl I'm sure you will figure something out, it's very similar.

Answer 2

Ok, Sarah, I made the changes to your code, now it displays binary, I added two variables, all the changes are pointed by little ◄■ arrows :

 .MODEL SMALL
 .STACK 100H

  .DATA
   PROMPT_1  DB  0DH,0AH,'Enter the character : $'
   PROMPT_2  DB  0DH,0AH,'The ASCII code of the given number in HEX       form     is : $'
   PROMPT_3  DB  0DH,0AH,'The ASCII code of the given number in BIN       form     is : $'
   MY_CHAR   DB  ?          ; ◄■ char entered by user.
   BINARY    DB  9 DUP('$') ; ◄■ zeroes and ones.

 .CODE
  MAIN PROC
 MOV AX, @DATA                ; initialize DS  
 MOV DS, AX

 @START:                      ; jump label 
   LEA DX, PROMPT_1           ; load and display the string PROMPT_1
   MOV AH, 9
   INT 21H

   MOV AH, 1                  ; read a character
   INT 21H                                      

   MOV MY_CHAR, AL ; ◄■ save char to use in binary conversion.
   MOV BL, AL                 ; move AL to BL

   CMP BL, 0DH                ; compare BL with CR
   JE @END                    ; jump to label @END if BL=CR

   LEA DX, PROMPT_2           ; load and display the string PROMPT_2
   MOV AH, 9
   INT 21H

   XOR DX, DX                 ; clear DX
   MOV CX, 4                  ; move 4 to CX

   @LOOP_1:                   ; loop label
     SHL BL, 1                ; shift BL towards left by 1 position
     RCL DL, 1                ; rotate DL towards left by 1 position
                              ; through carry
   LOOP @LOOP_1               ; jump to label @LOOP_1 if CX!=0

   MOV CX, 4                  ; move 4 to CX

   @LOOP_2:                   ; loop label
     SHL BL, 1                ; shift BL towards left by 1 position
     RCL DH, 1                ; rotate DH towards left by 1 position
                              ; through carry
   LOOP @LOOP_2               ; jump to label @LOOP_2 if CX!=0

   MOV BX, DX                 ; move DX to BX
   MOV CX, 2                  ; initialize loop counter

   @LOOP_3:                   ; loop label
     CMP CX, 1                ; compare CX wiht 1
     JE @SECOND_DIGIT         ; jump to label @SECOND_DIGIT if CX=1
     MOV DL, BL               ; move BL to DL
     JMP @NEXT                ; jump to label @NEXT

     @SECOND_DIGIT:           ; jump label
       MOV DL, BH             ; move BH to DL

     @NEXT:                   ; jump label

     MOV AH, 2                ; set output function

     CMP DL, 9                ; compare DL with 9
     JBE @NUMERIC_DIGIT       ; jump to label @NUMERIC_DIGIT if DL<=9
     SUB DL, 9                ; convert it to number i.e. 1,2,3,4,5,6
     OR DL, 40H               ; convert number to letter i.e. A,B...F
     JMP @DISPLAY             ; jump to label @DISPLAY

     @NUMERIC_DIGIT:          ; jump label
       OR DL, 30H             ; convert decimal to ascii code

     @DISPLAY:                ; jump label
       INT 21H                ; print the character
   LOOP @LOOP_3               ; jump to label @LOOP_3 if CX!=0


;▼ FROM CHAR TO BINARY ▼
     LEA SI, BINARY+7 ; ◄■ point to string in data segment.
     MOV CX, 8        ; ◄■ maximum number of binary digits.
   @BIN_CONVERSION:
     SHR MY_CHAR,1    ; ◄■ get rightmost bit.
     JC  @BIT1
     MOV [BYTE PTR SI], '0'
     JMP @BIN_SKIP
   @BIT1:
     MOV [BYTE PTR SI], '1'
   @BIN_SKIP:
     DEC SI
     LOOP @BIN_CONVERSION

     LEA DX, PROMPT_3 ; ◄■ display message.
     MOV AH, 9
     INT 21H         
     LEA DX, BINARY   ; ◄■ display binary.
     MOV AH, 9
     INT 21H         

   JMP @START                 ; jump to label @START

 @END:                        ; jump label

 MOV AH, 4CH                  ; return control to DOS
 INT 21H
 MAIN ENDP
 END MAIN