;*************************************************************************** ;This program intercepts Video I/O routine.Commands to scroll the screen and ;are intercepted,allothers passed through. This routine is attached to DOS. ;*************************************************************************** ;***** ***** ***** ***** ***** scrlky.asm ***** ***** ***** ***** ***** ***** ;----------------------------------------------------------------------------- ;INTERRUPT VECTORS FOR VIDEO AND KEYBOARD FUNCTIONS ;--------------------------------------------------------------------------- VECTORS SEGMENT AT 0 ORG 10H*4 VIDEO_INT LABEL DWORD ORG 16H*4 KEYBOARD_INT LABEL DWORD VECTORS ENDS ; ROM_BIOS_DATA SEGMENT AT 40H ORG 17H KB_FLAG DB ? ;bit 4 set for scroll lock ROM_BIOS_DATA ENDS ;--------------------------------------------------------------------------- ;Initialize vectors and attach to DOS ;--------------------------------------------------------------------------- CSEG SEGMENT PARA ASSUME CS:CSEG ORG 100H BEGIN: JMP INIT_VECTORS ;Initialize INT 10H and attach to DOS ;---------------------------------------------------------------------------- ;These memory locations store addresses of ROM routines for Video&KB I/O ;---------------------------------------------------------------------------- ROM_VIDEO_IO DD ;address of ROM routines ROM_KEYBOARD_IO DD SCROLL_COUNT DB 0 ;no. lines scrolled since last pause LAST_LOCK_STATE DB 0 ;scroll by 23 lines leaving one old line MAX_LINES DB 23 ;at the top of the screen LAST_LINE DB ;last line the cursor was one ;---------------------------------------------------------------------------- ;This routine intercepts calls to Video I/O routine in ROM ;Scroll Lock ; OFF This routine passes control directly to ROM BIOS ; ON Functions other than Scroll Up orScroll down are passed ; directly to ROM routines. Otherwise,this routine increments ; the scroll count and checks to see if it esceeds the page ; size of 25 lines. If so, loop until either shift key is ; pressed. ; left shift - allows scroll of entire window ; right shift- scroll one line ;---------------------------------------------------------------------------- INTERCEPT_VIDEO PROC FAR ASSUME CS:CSEG STI ;turn on interrupts again PUSH DS ;save registers used PUSH BX PUSH AX ASSUME DS:ROM_BIOS_DATA MOV BX,ROM_BIOS_DATA MOV DS,BX MOV AL,KB_FLAG ;check state of scroll lock key AND AL,10H ;pick off scroll lock bit ASSUME DS:CSEG MOV BX,CS ;Data segment for variables above MOV DS,BX CMP AL,LAST_LOCK_STATE JE UN_CHANGED MOV BL,MAX_LINES ;scroll lock key has changed,set to MOV SCROLL_COUNT,BL ;MAX_LINES to stop scrolling MOV LAST_LOCK_STATE,AL ;Save new scroll lock state PUSH CX ;read current cursro position PUSH DX PUSH AX MOV AH,3 MOV BH,0 PUSHF CALL ROM_VIDEO_IO ;find old cursor position MOV LAST_LINE,DH POP AX POP DX POP CX UN_CHANGED: XCHG AX,BX ;Recover function(AH) and retain scroll lock POP AX OR BL,BL ;is scroll lock on? JZ TO_VIDEO_IO ;no, jump to ROM video I/O ;---------------------------------------------------------------- ;Scroll Lock On ;---------------------------------------------------------------- CMP AH,2 ;check for SET CURSOR POSITION function JNE NOPE CMP DH,LAST_LINE ;is cursor beingmoved to next line? MOV LAST_LINE,DH ;save new cursor line JLE TO_VIDEO_IO ;no, go to ROM JMP SHORT CHECK_LOCK ;yes,see if need to lock NOPE: CMP AH,6 ;scroll up? JNE TO_VIDEO_IO ;no, ok to scroll ;yes,can't until shit key hit CHECK_LOCK: INC SCROLL_COUNT ;take care of scroll lock MOV BH,MAX_LINES CMP SCROLL_COUNT,BH ;have we scrolled more than MAX_LINES JL TO_VIDEO_IO ;no,its OK to scroll ;yes,can't scroll till shift key hit MOV BL,BH ;set scroll count to MAX_LINES-1 DEC BL ;so can print onemore line MOV SCROLL_COUNT,BL ASSUME DS:ROM_BIOS_DATA MOV BX,ROM_BIOS_DATA MOV DS,BX LOOP: MOV BL,KB_FLAG ;wait until right orleft shift key hit TEST BL,10H ;is scroll lock still on? JZ TO_VIDEO_IO AND BL,3 ;pick off shift key info JZ LOOP ;stay in loop until shift key pushed CMP BL,1 ;RIGHT SHIFT KEY HIT? JE SCROLL_LINE ;yes, scroll one line ;no,must be right shift key,reset scroll ct. XOR BX,BX MOV SCROLL_COUNT,BL SCROLL_LINE: ; TO_VIDEO_IO: POP BX PUSHF CALL ROM_VIDEO_IO POP DS IRET INTERCEPT_VIDEO ENDP ; ;---------------------------------------------------------------------------- ;If the KB function calls for a read (AH=0),then reset scroll count ;--------------------------------------------------------------------------- INTERCEPT_KEYBOARD PROC FAR ASSUME CS:CSEG,DS:CSEG STI PUSH DS ;save registers used this routine PUSH BX MOV BX,CS MOV DS,BX OR AH,AH ;check to see if AH=0-read character JNZ KB1 ;no,brancj off to KB I/O XOR BX,BX ;yes,set scroll count to 0 MOV SCROLL_COUNT,BL KB1: POP BX ASSUME DS:NOTHING POP DS JMP ROM_KEYBOARD_IO INTERCEPT_KEYBOARD ENDP ;----------------------------------------------------------------------- ;This section saves old interrupt vectors for KB and Video I/O.These vectors ;are replaced by addresses of INTERCEPT_VIDEO & INTERCEPT_KEYBPARD ;---------------------------------------------------------------------- INIT_VECTORS PROC NEAR ASSUME CS:CSEG,DS:CSEG MOV AH,3 ;set LAST_LINE to cursor line number XOR BH,BH INT 10H MOV LAST_LINE,DH ; ASSUME CS:CSEG,DS:VECTORS MOV AX,VECTORS MOV DS,AX ; MOV AX,VIDEO_INT ;save address of ROM routines MOV ROM_VIDEO_IO,AX MOV AX,VIDEO_INT[2] MOV ROM_VIDEO_IO[2],AX MOV AX,OFFSET INTERCEPT_VIDEO ;set video INT 10H to point MOV VIDEO_INT,AX ;to INTERCEPT_VIDEO above MOV VIDEO_INT[2],CS ; MOV AX,KEYBOARD_INT ;save address of the ROM routines MOV ROM_KEYBOARD_IO,AX MOV AX,KEYBOARD_INT[2] MOV ROM_KEYBOARD_IO[2],AX MOV AX,OFFSET INTERCEPT_KEYBOARD ;set KB INT 16H to point to MOV KEYBOARD_INT,AX ;INTERCEPT_KEYBOARD above MOV KEYBOARD_INT[2],CS ; MOV DX,OFFSET INIT_VECTORS ;end of resident portion INT 27H ;terminate but stay resident INIT_VECTORS ENDP ; CSEG ENDS END BEGIN