CODEWITHSUNDEEP
assemblyx86vgadosbox
BCRwar1
BCRwar1

Reputation: 189

Assembly Language Changing Color Of Characters

This is a basic DOSBox program that when executed will flip the screen from left to right. The program works fine. The only problem I am having is I am supposed to make all non-alphabetic characters be red on white. I don't have any trouble changing the color of non-alphabetic characters but I do not know the combination for binary red on white. I thought it was 11111100b but this makes the color red on grey and the characters blink on and off. Probably something very simple but I can't figure it out. Any suggestions?

MyCode SEGMENT
        ASSUME CS:MyCode, DS:MyData   

MainProg  PROC                

    MOV     AX, MyData             
    MOV     DS, AX                 
    MOV     AX, 0B800h         
    MOV     ES, AX

    MOV BX, (25 * 160)                  ;BX contains value that equals row 25, column 0


    loop25: 

      SUB BX, 160                       ;Selects next row
      CALL flipRow                      ;Flips that row

      CMP BX, 0                         ;Have all rows been flipped?
    JNE loop25                          ;if not, repeat

    MOV     AH, 4Ch                
    INT     21h                   

MainProg ENDP  

flipRow  PROC                           ;PROC will flip each rown on verticle axis

    MOV DI, BX                          ;Puts row, column 0 in DI
    ADD DI, 158                         ;Adds 158 to DI to select right most character
    MOV SI, BX                          ;Puts row, column 0 in SI

 loopRow:                               ;loop until row is finished flipping

    MOV AX, ES: [DI]                    ;AX points to right most character
    MOV CX, ES: [SI]                    ;CX points to left most character
    MOV ES: [DI], CX                    ;Put left most character into right most place
  ;-------------------------------------------------------------------------
  CMP CL, 65                                 
  JL thenPart
  CMP CL, 91
  JL next
  CMP CL, 97
  JL thenPart                            ;Is the character Alphebetic? If not, color red on white
  CMP CL, 123                  
  JL next
  CMP CL, 122
  JG next
  thenPart:                                   
    MOV ES: [DI + 1], BYTE PTR 00FCh
  next:
  ;-------------------------------------------------------------------------
    MOV ES: [SI], AX                     ;Put right most character in left most place
  ;-------------------------------------------------------------------------
  CMP AL, 66                                
  JL then2
  CMP AL, 91
  JL next2
  CMP AL, 97
  JL then2                               ;Is the character Alphabetic? If not, color red on white
  CMP AL, 123
  JL next2
  CMP AL, 122
  JG next2
  then2:                                   
    MOV ES: [SI + 1], BYTE PTR 01111100b
  next2:
  ;-------------------------------------------------------------------------
    DEC DI
    DEC DI                               ;Move in left
    INC SI
    INC SI                               ;Move in right

  CMP SI, DI                             ;Is the row completely flipped? 
  JL loopRow                             ;If not, repeat
    RET
flipRow ENDP                 

MyCode ENDS

Upvotes: 0

Views: 3122

Answers (1)

Jongware
Jongware

Reputation: 22457

The CGA/EGA/VGA screen adapter for which this color system was designed, had two distinctive text color modes.

In its default mode, the foreground color has a 'bright' bit -- the 3rd bit, where 2-1-0 are for RGB --, but this same bit in the 'background' part is 'blink'. So effectively you cannot have a 'bright' background.

The default setting can be changed with a low-level VIDEO interrupt:

   AX = 1003h (operation code)
   BL = 00h (enable bold background)
or BL = 01h (enable blinking)
   INT 10h (execute operation)

(Ancient memory jogged ctsy. of http://webpages.charter.net/danrollins/techhelp/0140.HTM.)

Upvotes: 1

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