; This file was taken from Michael Abrash' XSHARP package, a library ; for programming mode X (320x240x256). ; Mode X (320x240, 256 colors) mode set routine. Works on all VGAs. ; C near-callable as: ; void Set320x240Mode(void); ; Tested with TASM 2.0. ; Modified from public-domain mode set code by John Bridges. 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 .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) .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) mov ax,13h ;let the BIOS set standard 256-color int 10h ; mode (320x200 linear) mov dx,SC_INDEX mov ax,0604h out dx,ax ;disable chain4 mode mov ax,0100h out dx,ax ;synchronous reset while switching clocks mov dx,MISC_OUTPUT mov al,0e7h out dx,al ;select 28 MHz dot clock & 60 Hz scanning rate mov dx,SC_INDEX mov ax,0300h out dx,ax ;undo reset (restart sequencer) 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 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 pop di ;restore C register vars pop si pop bp ;restore caller's stack frame ret _Set320x240Mode endp end