Mail Archives: djgpp/1997/05/03/18:06:47
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> Hi,
>
> What's ModeX? Is it the SVGA modes (i.e. 640x480x256, 800x600x65536,etc.)?
>
> Thanks!
> Bye!
Mode-X is a term first coined by Michael Abrash. He discovered this video
mode independently, however he was not the first to discover it. He was
merely the first to name it and release code in Dr. Dobb's Journal. Mode-X
is a 320x240x256-color mode. It has several advantages because of it's
square pixels (1:1 aspect ratio) and its page size makes it ideal for
page-flipping. With the use of latches and off-screen memory, you may copy
images four pixels at a time. Attached is a all-assembly code to select
Mode-X (You wouldn't want to cheat and use allegro now would you?)
it is C near-callable as void Set320x240Mode(void). ENJOY!
~Chris Myers (3D.Mug)
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name="L32-1.ASM"
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; Mode X (320x240, 256 colors) mode set routine. Works on all VGAs.
; ****************************************************************
; * Revised 6/19/91 to select correct clock; fixes vertical roll *
; * problems on fixed-frequency (IBM 851X-type) monitors. *
; ****************************************************************
; C near-callable as:
; void Set320x240Mode(void);
; Tested with TASM 4.0 by Jim Mischel 12/16/94.
; Modified from public-domain mode set code by John Bridges.
=0D
SC_INDEX equ 03c4h ;Sequence Controller Index
CRTC_INDEX equ 03d4h ;CRT Controller Index
MISC_OUTPUT equ 03c2h ;Miscellaneous Output register
SCREEN_SEG equ 0a000h ;segment of display memory in mode X
=0D
.model small
.data
; Index/data pairs for CRT Controller registers that differ between
; mode 13h and mode X.
CRTParms label word
dw 00d06h ;vertical total
dw 03e07h ;overflow (bit 8 of vertical counts)
dw 04109h ;cell height (2 to double-scan)
dw 0ea10h ;v sync start
dw 0ac11h ;v sync end and protect cr0-cr7
dw 0df12h ;vertical displayed
dw 00014h ;turn off dword mode
dw 0e715h ;v blank start
dw 00616h ;v blank end
dw 0e317h ;turn on byte mode
CRT_PARM_LENGTH equ (($-CRTParms)/2)
=0D
.code
public _Set320x240Mode
_Set320x240Mode proc near
push bp ;preserve caller's stack frame
push si ;preserve C register vars
push di ; (don't count on BIOS preserving anything)
=0D
mov ax,13h ;let the BIOS set standard 256-color
int 10h ; mode (320x200 linear)
=0D
mov dx,SC_INDEX
mov ax,0604h
out dx,ax ;disable chain4 mode
mov ax,0100h
out dx,ax ;synchronous reset while setting Misc Output
; for safety, even though clock unchanged
mov dx,MISC_OUTPUT
mov al,0e3h
out dx,al ;select 25 MHz dot clock & 60 Hz scanning rate
=0D
mov dx,SC_INDEX
mov ax,0300h
out dx,ax ;undo reset (restart sequencer)
=0D
mov dx,CRTC_INDEX ;reprogram the CRT Controller
mov al,11h ;VSync End reg contains register write
out dx,al ; protect bit
inc dx ;CRT Controller Data register
in al,dx ;get current VSync End register setting
and al,7fh ;remove write protect on various
out dx,al ; CRTC registers
dec dx ;CRT Controller Index
cld
mov si,offset CRTParms ;point to CRT parameter table
mov cx,CRT_PARM_LENGTH ;# of table entries
SetCRTParmsLoop:
lodsw ;get the next CRT Index/Data pair
out dx,ax ;set the next CRT Index/Data pair
loop SetCRTParmsLoop
=0D
mov dx,SC_INDEX
mov ax,0f02h
out dx,ax ;enable writes to all four planes
mov ax,SCREEN_SEG ;now clear all display memory, 8 pixels
mov es,ax ; at a time
sub di,di ;point ES:DI to display memory
sub ax,ax ;clear to zero-value pixels
mov cx,8000h ;# of words in display memory
rep stosw ;clear all of display memory
=0D
pop di ;restore C register vars
pop si
pop bp ;restore caller's stack frame
ret
_Set320x240Mode endp
end
=0D
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