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Assembler

The EGA has a nice underline feature. If you send the video card a certain code, you can have certain characters underlined.

Listing 1 below is the code to set the EGA card. Listing 2 (at right) is some demo code to show you what is being done.

Typing UNDER1 at the DOS prompt will "turn it on". Typing UNDER1 N at the DOS prompt will "turn it off". First enter UNDER1 at the DOS prompt. Then enter UNDER2 to see the text. Now enter UNDER1 N and UNDER1 each in turn to see the underline appear and disappear.

 ;; Listing 1
.model tiny
.code

           mov  al,[5Dh]  ; the 'N' in the FCB
           xor  bx,bx     ;  could use [82h]
           mov  ds,bx
           mov  ah,[0485h]
           cmp  al,4Eh
           jz   NotN
           dec  ah
NotN:      mov  dx,[0463h]
           mov  al,14h
           out  dx,ax
           ret
.end

 ;; Listing 2
.model tiny
.code

           mov  ax,0600h
           mov  bh,02h
           xor  cx,cx
           mov  dx,1950h
           int  10h
           mov  ah,02
           xor  bh,bh
           xor  dx,dx
           int  10h
           mov  ax,0950h
           mov  bx,0001
           mov  cx,0028h
           int  10h
           mov  ah,02
           mov  dx,0028h
           int  10h
           mov  ax,0943h
           mov  bl,02h
           int  10h
           ret
.end

Please note that this will only work on an EGA or better card. ¥

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