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[16.git] / 16 / scrasm / MODEX.INC

diff --git a/16/scrasm/MODEX.INC b/16/scrasm/MODEX.INC
new file mode 100755 (executable)
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+; ====================================================================\r
+; Entry points:\r
+; ====================================================================\r
+MODEX_START     MACRO\r
+                mov     ax,13h  ;let the BIOS set standard 256-color\r
+                int     10h     ; mode (320x200 linear)\r
+;               PALETTE_BLACK\r
+                call    ModifyForX\r
+                ENDM\r
+\r
+; ====================================================================\r
+; This is MODE-X code from Dr. Dobb's Journal, by Michael Abrash.\r
+; I modified it from 320x240 back to 320x200, and then to 512 virtual\r
+; width, for scrolling purposes.\r
+; ====================================================================\r
+\r
+; Mode X (320x240, 256 colors) mode set routine. Works on all VGAs.\r
+; ****************************************************************\r
+; * Revised 6/19/91 to select correct clock; fixes vertical roll *\r
+; * problems on fixed-frequency (IBM 851X-type) monitors.        *\r
+; ****************************************************************\r
+; Modified from public-domain mode set code by John Bridges.\r
+\r
+; Index/data pairs for CRT Controller registers that differ between\r
+; mode 13h and mode X.\r
+CRTParms label  word\r
+;       dw      00d06h  ;vertical total\r
+;       dw      03e07h  ;overflow (bit 8 of vertical counts)\r
+;       dw      04109h  ;cell height (2 to double-scan)\r
+;       dw      0ea10h  ;v sync start\r
+;       dw      0ac11h  ;v sync end and protect cr0-cr7\r
+;       dw      0df12h  ;vertical displayed = 480\r
+        dw      00014h  ;turn off dword mode                    *\r
+;       dw      0e715h  ;v blank start\r
+;       dw      00616h  ;v blank end\r
+        dw      0e317h  ;turn on byte mode                      *\r
+\r
+        dw      (VIRTUAL_WIDTH*32)+13h  ; width of screen = VWid   NEW\r
+;       dw      09012h  ;vertical displayed = 400 (already like this)\r
+CRT_PARM_LENGTH equ     (($-CRTParms)/2)\r
+\r
+ModifyForX      PROC    near\r
+                mov     dx,SC_INDEX\r
+                mov     ax,0604h\r
+                out     dx,ax           ;disable chain4 mode\r
+                mov     ax,0100h\r
+                out     dx,ax           ;synchronous reset while setting Misc\r
+                                        ; Output for safety, even though clock\r
+                                        ; unchanged\r
+                mov     dx,MISC_OUTPUT\r
+                mov     al,0e3h\r
+                out     dx,al           ;select 25 MHz dot clock & 60 Hz scanning rate\r
+\r
+                mov     dx,SC_INDEX\r
+                mov     ax,0300h\r
+                out     dx,ax           ;undo reset (restart sequencer)\r
+\r
+                mov     dx,CRTC_INDEX   ;reprogram the CRT Controller\r
+                mov     al,11h          ;VSync End reg contains register write\r
+                out     dx,al           ; protect bit\r
+                inc     dx              ;CRT Controller Data register\r
+                in      al,dx           ;get current VSync End register setting\r
+                and     al,7fh          ;remove write protect on various\r
+                out     dx,al           ; CRTC registers\r
+                dec     dx              ;CRT Controller Index\r
+                cld\r
+                push    cs\r
+                pop     ds\r
+                mov     si,offset CRTParms ;point to CRT parameter table\r
+                mov     cx,CRT_PARM_LENGTH ;# of table entries\r
+SetCRTParmsLoop:\r
+                lodsw                   ;get the next CRT Index/Data pair\r
+                out     dx,ax           ;set the next CRT Index/Data pair\r
+                loop    SetCRTParmsLoop\r
+\r
+                mov     dx,SC_INDEX\r
+                mov     ax,0f02h\r
+                out     dx,ax           ;enable writes to all four planes\r
+                mov     ax,SCREEN_SEG   ;now clear all display memory, 8 pixels\r
+                mov     es,ax           ; at a time\r
+                sub     di,di           ;point ES:DI to display memory\r
+                sub     ax,ax           ;clear to zero-value pixels\r
+                mov     cx,8000h        ;# of words in display memory\r
+            rep stosw                   ;clear all of display memory\r
+\r
+                ret\r
+ModifyForX      ENDP\r
+\1a
\ No newline at end of file