103 lines
4.5 KiB
NASM
103 lines
4.5 KiB
NASM
;
|
|
input equ 080h ;command line tail buffer
|
|
cr equ 0dh ;ASCII carriage return
|
|
;
|
|
cseg segment byte
|
|
assume cs:cseg,ds:cseg
|
|
;
|
|
org 0100h ;since this will be
|
|
; a COM file
|
|
;
|
|
clear: ;initialize display...
|
|
;call BIOS video driver to
|
|
mov ah,15 ;get current display mode:
|
|
int 10h ;returns AL = mode, and
|
|
;AH = no. of columns.
|
|
cmp al,7 ;if we are in graphics modes
|
|
je clear0 ;(modes 4,5,6) then exit
|
|
cmp al,3 ;but if we are in mode 0-3
|
|
ja clear9 ;or 7 then continue.
|
|
clear0: ;set up size of window to
|
|
;be initialized...
|
|
xor cx,cx ;set upper left corner of
|
|
;window to (X,Y)=(0,0)
|
|
mov dh,24 ;set Y to 24 for lower right
|
|
mov dl,ah ;corner, and X to the number
|
|
dec dl ;of columns returned by BIOS
|
|
;minus 1
|
|
mov bh,7 ;initialize attribute byte
|
|
;to "normal" video display,
|
|
;i.e. white on black.
|
|
;set SI=address of command
|
|
;tail's length byte
|
|
mov si,offset input
|
|
cld ;clear the Direction Flag
|
|
;for "LODS" string instruction.
|
|
lodsb ;check length byte to see if
|
|
or al,al ;there's any command tail.
|
|
jz clear8 ;no,go clear the screen
|
|
;with normal video attribute
|
|
;
|
|
clear1: lodsb ;check the next byte of
|
|
;the command tail,
|
|
cmp al,cr ;if carriage return
|
|
je clear8 ;we are done.
|
|
or al,20h ;fold the character to
|
|
;lower case.
|
|
cmp al,'a' ;make sure it's in range a-z
|
|
jb clear1 ;no, skip it
|
|
cmp al,'z'
|
|
ja clear1 ;no, skip it
|
|
cmp al,'i' ;I=Set intensity
|
|
jne clear2 ;jump if not I
|
|
or bh,08 ;set intensity bit
|
|
jmp short clear1
|
|
clear2: cmp al,'r' ;R=Reverse
|
|
jne clear3 ;jump if not R
|
|
and bh,088h ;mask off old foreground/
|
|
;background bits and
|
|
or bh,070h ;change to reverse video
|
|
jmp short clear1
|
|
clear3: cmp al,'u' ;U=Underline
|
|
jne clear4 ;jump if not U
|
|
and bh,088h ;mask off old foreground/
|
|
;background bits and
|
|
or bh,01h ;change to underline
|
|
jmp short clear1
|
|
clear4: cmp al,'b' ;B=Blink
|
|
jne clear5 ;jump if not B
|
|
or bh,080h ;set blink bit
|
|
jmp short clear1
|
|
clear5: cmp al,'s' ;S=Silent
|
|
jne clear1 ;if not S try next char.
|
|
mov bh,0 ;if S command, rig for
|
|
;silent running. Clear
|
|
;the foreground/background
|
|
;display control fields, and
|
|
;don't bother to look for
|
|
;any more command characters.
|
|
;
|
|
clear8: ;now we have decoded all
|
|
;the characters in the
|
|
;command tail, and are ready
|
|
;to initialize the display.
|
|
;BH= desired attribute
|
|
;CL,CH=(X,Y),upper left
|
|
; corner of window
|
|
;DL,DH=(X,Y),lower right
|
|
; corner of window
|
|
mov ax,0600h ;AH = function type 6,
|
|
;AL = lines to scroll (zero)
|
|
int 10h ;request initialization
|
|
;of window by BIOS
|
|
;
|
|
mov ah,2 ;now set the cursor to
|
|
mov bh,0 ;(X,Y)=(0,0), Page=0
|
|
xor dx,dx
|
|
int 10h
|
|
;
|
|
clear9: int 20h ;exit to PC-DOS
|
|
;
|
|
cseg ends
|
|
;
|
|
end clear |