Category : Files from Magazines
Archive   : PJ-VGA.ZIP
Filename : VGA64-L3.ASM

 
Output of file : VGA64-L3.ASM contained in archive : PJ-VGA.ZIP
; *** Listing 3 ***
;
; Program that draws a diagonal line to illustrate the use of a
; Color Don't Care register setting of 0FFh to support fast
; read-modify-write operations to VGA memory in write mode 3 by
; drawing a diagonal line.
;
; Note: Works on VGAs only.
;
; By Michael Abrash 4/2/88
;
stack segment word stack 'STACK'
db 512 dup (?)
stack ends
;
VGA_SEGMENT EQU 0a000h
SCREEN_WIDTH EQU 80 ;in bytes
GC_INDEX EQU 3ceh ;Graphics Controller Index register
SET_RESET EQU 0 ;Set/Reset register index in GC
ENABLE_SET_RESET EQU 1 ;Enable Set/Reset register index in GC
GRAPHICS_MODE EQU 5 ;Graphics Mode register index in GC
COLOR_DONT_CARE EQU 7 ;Color Don't Care register index in GC
;
code segment word 'CODE'
assume cs:code
Start proc near
;
; Select graphics mode 12h.
;
mov ax,12h
int 10h
;
; Select write mode 3 and read mode 1.
;
mov dx,GC_INDEX
mov al,GRAPHICS_MODE
out dx,al
inc dx
in al,dx ;VGA registers are readable, bless them!
or al,00001011b ;bit 3=1 selects read mode 1, and
; bits 1 & 0=11 selects write mode 3
jmp $+2 ;delay between IN and OUT to same port
out dx,al
dec dx
;
; Set up set/reset to always draw in white.
;
mov al,SET_RESET
out dx,al
inc dx
mov al,0fh
out dx,al
dec dx
mov al,ENABLE_SET_RESET
out dx,al
inc dx
mov al,0fh
out dx,al
dec dx
;
; Set Color Don't Care to 0, so reads of VGA memory always return 0FFh.
;
mov al,COLOR_DONT_CARE
out dx,al
inc dx
sub al,al
out dx,al
;
; Set up the initial memory pointer and pixel mask.
;
mov ax,VGA_SEGMENT
mov ds,ax
sub bx,bx
mov al,80h
;
; Draw 400 points on a diagonal line sloping down and to the right.
;
mov cx,400
DrawDiagonalLoop:
and [bx],al ;reads display memory, loading the latches,
; then writes AL to the VGA. AL becomes the
; bit mask, and set/reset provides the
; actual data written
add bx,SCREEN_WIDTH
; point to the next scan line
ror al,1 ;move the pixel mask one pixel to the right
adc bx,0 ;advance to the next byte if the pixel mask wrapped
loop DrawDiagonalLoop
;
; Wait for a key to be pressed to end, then return to text mode and
; return to DOS.
;
WaitKeyLoop:
mov ah,1
int 16h
jz WaitKeyLoop
sub ah,ah
int 16h ;clear the key
mov ax,3
int 10h ;return to text mode
mov ah,4ch
int 21h ;done
Start endp
code ends
end Start



  3 Responses to “Category : Files from Magazines
Archive   : PJ-VGA.ZIP
Filename : VGA64-L3.ASM

  1. Very nice! Thank you for this wonderful archive. I wonder why I found it only now. Long live the BBS file archives!

  2. This is so awesome! 😀 I’d be cool if you could download an entire archive of this at once, though.

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