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title DOORS.ASM - Switch Color/Mono Screens On Keyboard Request
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;
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VECTORS segment at 0h ; 8088 / 80286 Interrupt Vector Area
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org 9h*4 ; IBM PC Keyboard is Int 9H
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KB_INT_VECTOR label dword ; Double word label
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;
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VECTORS ends
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;
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ROM_BIOS_DATA segment at 40h ; Low Memory "BIOS" Parameters
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;
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org 10h ; Location of EQUIP_FLAG
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EQUIP_FLAG dw ? ; Contains video settings
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; in bits 4 and 5
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;
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org 17h ; Location of KB_FLAG
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KB_FLAG db ? ; Contains Alt (bit 3) &
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; Right Shift (bit 0) States
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ROM_BIOS_DATA ends
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;
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; Initialization Routine
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;
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CODE_SEG segment
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assume cs:CODE_SEG
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org 100h ; COM program format
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BEGIN: jmp SWAP_VECTORS ; Initialize vectors and attach to DOS
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;
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ROM_KB_INT dd 0 ; Double word to save address of
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; ROM-BIOS keyboard interrupt
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; DOORS_INT intercepts the keyboard interrupt and switches
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; screens if [Alt]-[Right Shift] combination is pressed
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;
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DOORS_INT proc near
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assume ds:nothing
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push ds ; Push all affected registers
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push es
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push ax
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push bx
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push cx
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push dx
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push si
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push di
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;
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pushf ; Push Flags for fake interrupt call
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call ROM_KB_INT ; to BIOS program to read keyboard
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;
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assume ds:ROM_BIOS_DATA ; Define data segment to read
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mov ax,ROM_BIOS_DATA ; keyboard flag & equipment flag
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mov ds,ax
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mov al,KB_FLAG ; Get keyboard flag
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and al,09h ; Isolate [Alt] + [Right Shift]
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cmp al,09h ; Are they pressed?
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jne RETURN ; No, quit
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;
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; [Alt] + [Right Shift] are pressed -- Continue processing
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; Check on video mode - quit if not monochrome, color 80x25 or BW 80x25
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;
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mov ah,15 ; Call Func 15 of Int 10h to
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int 10h ; get video state of the PC
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cmp al,7 ; Is screen monochrome?
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je SCREEN_OKAY ; Yes, go switch screens
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cmp al,3 ; Is screen color text?
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jbe CHECK_40_OR_80 ; Yes, go check for 80 or 40 char
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jmp RETURN ; Screen is in graphics mode, quit
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CHECK_40_or_80:
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cmp al,1 ; Is screen 40-character?
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jbe RETURN ; Yes, quit
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;
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SCREEN_OKAY:
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;
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; Save the current cursor position
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;
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mov ah,3 ; Call Func 3 of Int 10H
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mov bh,0 ; to read cursor position
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int 10h ; (page zero for color screen)
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;
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; Screen switch routine - Establish calling argument (AL) for Int 10h
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;
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mov bx,EQUIP_FLAG ; Current equipment flag to BX
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mov cx,bx ; Make a copy of it in CX
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and cx,30h ; Extract screen information
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xor bx,cx ; Erase current screen information in BX
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or bx,20h ; Set BX to color 80x25
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mov al,3 ; Set AL for color 80x25 in Int 10h
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cmp cx,30h ; Is current mono?
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je SET_MODE ; Yes, switch to color
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or bx,30h ; No, set BX for monochrome
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mov al,7 ; Set AL for monochrome in Int 10h
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SET_MODE:
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mov EQUIP_FLAG,bx ; Write BX to equipment flag
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xor ah,ah ; Use Func 0 of Int 10h to
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int 10h ; change screen parameters
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;
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; Restore Cursor
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;
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mov ah,2 ; Use Func 2 of Int 10h to restore
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mov bh,0 ; cursor on new screen (position in DX)
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int 10h
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;
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; After screens are switched, set DS and ES registers to move screen data
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;
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mov ax,0b000h ; Load ES with Mono Segment
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mov es,ax
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mov ax,0b800h ; Load DS with Color Segment
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mov ds,ax
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cmp cx,30h ; Did we switch from mono?
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jne COPY_THE_SCREEN ; Yes, move data from mono to color
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push ds ; No, swap ES and DS to move data
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push es ; from color to mono
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pop ds
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pop es
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COPY_THE_SCREEN:
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xor di,di ; Start at zero offsets
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xor si,si
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mov cx,2000 ; 2000 chars + attrs per screen
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cld ; Make sure move is 'forward'
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rep movsw ; Move Words with string instruction
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;
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RETURN:
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pop di ; Restore saved registers
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pop si
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pop dx
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pop cx
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pop bx
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pop ax
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pop es
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pop ds
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iret ; Return to system
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DOORS_INT endp
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;
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; This procedure initializes the new keyboard interupt vectors
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;
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SWAP_VECTORS proc near
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assume ds:VECTORS
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mov ax,VECTORS ; Set up the data
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mov ds,ax ; segment for vectors
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cli ; Disable interrupts
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mov ax,word ptr KB_INT_VECTOR ; Store addresses
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mov word ptr ROM_KB_INT,ax ; of BIOS program
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mov ax,word ptr KB_INT_VECTOR[2]
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mov word ptr ROM_KB_INT[2],ax
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mov word ptr KB_INT_VECTOR, offset DOORS_INT ; Substitute Our
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mov word ptr KB_INT_VECTOR[2],cs ; Program
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sti ; Enable interrupts
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mov dx,offset SWAP_VECTORS ; End of new resident
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; program
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int 27h ; Terminate resident
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SWAP_VECTORS endp
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CODE_SEG ends
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end BEGIN
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;
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