; page 66,132 ; ;SCRNOFF3.ASM for the IBM PC/XT & PCJR - 1987 by Ocean ; ;This is part 1 of a 2 part utilities set consisting of ----------------------- ;SCRNOFF3.ASM & KYLOCK.ASM. --------------------- THEY MUST BE USED TOGETHER! ; ----------------------- ; eoi equ 20h ;end-of-interrupt signal int_ctrl_port equ 20h ;8259 interrupt controller port ; code segment para public 'code' assume cs:code org 0 seg_org equ $ ; bios_data segment at 40h ;bios data area org 063h addr_6845 dw ? ;define location that holds ;word address of active display org 065h crt_mode_set db ? ;define location that holds ;byte loaded into pc active ;display port or pcjr's vga bios_data ends ; org 0100h begin: jmp initialize ;goto initialization routine ; adapter db 0 ;0 = EGA, 1 = CGA or MDA, and ;2 = PCJR pcjr_mode db ? ;current setting of PCJR video pc_mode db ? ;current setting of 6845 mode ;control register of the pc count dw 0cc8h ;initial 3 min. to blank screen timer_stat db 01h ;initialize timer - on msr_address dw ? ;address of mode select register pcjr_signature db 0fdh ;PCJR BIOS signature ibm_signature db 'IBM' ;EGA BIOS signature errmsg db 13,10,'SCRNOFF3 ALREADY LOADED!',13,10,'$' ; old_int_1ch label dword ;holding area for INT 8h vector int_1ch_ptr dw 2 dup (?) old_int_16h label dword ;holding area for INT 16h vector int_16h_ptr dw 2 dup (?) ; ;------------------------------------------------------------------------------ ;All calls to INT 16h will henceforth be routed thru here. If ah = 255 on ;entry, bh is set to 255 to signal the caller that this routine was indeed ;invoked. ;------------------------------------------------------------------------------ new_int_16h proc near cmp ah,127 ;ah = 127? jne switch ;no, then jump mov bh,ah ;yes, set bh to 255 and exit iret switch: cmp ah,158 ;INT called by ALT O keypress? jne newint1 ;no, then jump add timer_stat,01h ;yes, toggle timer on/off iret newint1: jmp old_int_16h ;goto normal 16h handler new_int_16h endp ; ;------------------------------------------------------------------------------ ;User timer INT 1Ch is now routed through here. ;------------------------------------------------------------------------------ ; countdown3 proc near test timer_stat,01h ;timer activated? jz do_nothing ;no, exit cmp count,00 ;yes, check if count has zeroed jz do_nothing ;already zero, exit dec count ;active & not zero, tick & ... jnz do_nothing ;not zero, exit ... else ... ; ;Time has run out, call the video_disable routine to blank the screen only. ;The rest of the program is still ready to lock the keyboard with a password if ;desired. ; push ax ;save ax register push dx ;save dx register cli ;disable all interrupts call video_disable ;time is up - disable the video mov al,eoi ;get eoi value out int_ctrl_port,al ;send eoi signal to the 8259 pop dx ;restore dx register pop ax ;restore ax register sti do_nothing: jmp old_int_1ch ;iret thru old_int_1Ch countdown3 endp ; ;------------------------------------------------------------------------------ ;This routine is user vector interrupt 4dh! ;------------------------------------------------------------------------------ unblank proc near cmp count,00 ;if timer is not 0 the screen ;is still visible - jump to jnz reset_count ;reset count to 3 min., since ;a keypress has occured push ax ;save ax register push dx ;save dx register call video_enable ;timer was 0 when a keypress ;occured, so make the screen ;visible pop dx ;restore dx register pop ax ;restore ax register reset_count: mov count,0cc8h ;reset timer to 3 min. then ;return to caller (KYLOCK.COM) iret unblank endp ; ;------------------------------------------------------------------------------ ;VIDEO ENABLE and VIDEO DISABLE enable and disable the VIDEO output to the ;screen of the PCJR ;------------------------------------------------------------------------------ ; video_disable proc near ;disable the video display cmp adapter,0 ;is video adapter an EGA? je ega_disable ;yes, then jump test adapter,2 ;is computer a PCJR? jnz jr_disable ;yes, then jump ; ;Disable video of PC with CGA or MDA adapter. ; push ds ;save ds mov ax,bios_data ;set es to bios data area mov ds,ax assume ds:bios_data mov al,crt_mode_set ;get current value (dynamic) of ;6845 mode control register mov pc_mode,al ;save it mov ax,addr_6845 ;get active display address add ax,4 ;add 4 to get MSR address mov msr_address,ax ;save address mov al,0ah ;out 6845 index register... mov dx,03b4h ;points to 6845 data reg. 10 out dx,al mov al,2bh ;value to turn off cursor mov dx,03b5h ;6845 data registers port out dx,al ;disable cursor mov dx,msr_address ;6845 mode control register mov al,pc_mode ;get current value of 6845 mode and al,37h ;strip enable bit out dx,al ;disable video display pop ds ;restore ds ret ; ;disable video of PC with an EGA card. ; ega_disable: xor al,al ;zero al (clear bit 5) call set_ega ;disable EGA ret ; ;Disable video of PCJR. ; jr_disable: push ds ;save ds register mov ax,bios_data ;set es to bios data area mov ds,ax ; assume ds:bios_data ; mov al,crt_mode_set ;get current value (dynamic) of ;PCJR VGA mode control register mov pcjr_mode,al ;store current value, VGA mode mov dx,03dah ;PCJR VGA I/O port in al,dx ;addr/data f/f to proper state mov al,02h ;VGA border color register out dx,al ;set VGA to border color cont. mov al,00h ;color black out dx,al ;set border color black mov al,00 ;VGA mode control 1 register out dx,al ;set VGA to mode control 1 mov al,pcjr_mode ;get current value of VGA mode and al,0f7h ;strip enable bit out dx,al ;disable video display pop ds ;restore ds register ret video_disable endp ; video_enable proc near ;enable the video display cmp adapter,0 ;is video adapter an EGA? je ega_enable ;yes,then jump test adapter,2 ;is the computer a PCJR? jnz jr_enable ;yes, then jump ; ;Enable video of PC with CGA or MDA adapter card. ; mov al,0ah ;out 6845 index register... mov dx,03b4h ;points to 6845 data reg. 10 out dx,al mov al,0bh ;value to turn cursor on mov dx,03b5h ;6845 data registers port out dx,al ;enable cursor mov dx,msr_address ;6845 mode control register mov al,pc_mode ;get stored value 6845 mode out dx,al ;enable pc display ret ; ;Enable video of PC with an EGA adapter card. ; ega_enable: mov al,20h ;set bit 5 of al call set_ega ;enable EGA video ret ; ;Enable video of PCJR. ; jr_enable: mov dx,03dah ;set PCJR VGA address in al,dx ;addr/data f/f to proper state mov al,00h ;VGA mode control 1 register out dx,al ;set VGA to mode control 1 mov al,pcjr_mode ;get stored value VGA mode out dx,al ;enable PCJR video display ... ;border remains black ret video_enable endp ; ;----------------------------------------------------------------------------- ;SET_EGA is called by VIDEO_ENABLE and VIDEO_DISABLE routines to selectively ;set or clear bit 5 of the EGA Attribute Address Register. ;Entry: AL - value to OUT to Attribute Address Register ;----------------------------------------------------------------------------- ; set_ega proc near push ax ;save AL mov dx,3bah ;reset monochrome flip-flop... in al,dx ;for write to Address Register mov dx,3dah ;reset color flip-flop in al,dx mov dx,3c0h ;set DX to Attr Addr Register pop ax ;retrieve entry value of AL out dx,al ;write value to register ret set_ega endp ; ;------------------------------------------------------------------------------ ;INITIALIZE routine checks if SCRNOFF3 has already been loaded. If it has, ;execution aborts with an error message. If it hasn't, then the value of ;ADAPTER is set according to the type of display adapter present in the system ;and the vectors in low memory pointing to the INT 9h and 16h routines are set ;to point to our own newly installed code. ;------------------------------------------------------------------------------ ; initialize proc near ; ;See if SCRNOFF3 has been previously loaded by calling INT 16h with AH set to ;254 and BH set to 0. If BH comes back unchanged, then SCRNOFF3 is NOT ;currently resident in memory; if BH = 255, then SCRNOFF3 has been loaded. ; mov ah,127 ;set AH and BH xor bh,bh int 16h ;call interrupt routine or bh,bh ;is BH = 0? je init1 ;yes, then continue lea dx,errmsg ;no, print error message & exit mov ah,09h int 21h ret ; ;Check the computer's ID to see if its a PC or PCJR. ; init1: mov ax,0f000h ;es to BIOS segment holding mov es,ax ;computer ID value mov al,byte ptr es:[0fffeh] ;offset address and load to al sub al,0fch ; or al,al ;al = 0? jz pc ;AT, try the pc routine... dec al ;al = 1? jz pcjr ;yes, then computer is a PCJR dec al ;al = 2? jz pc ;XT, try the PC routine... dec al ;al = 3? jz pc ;PC jnz pc ;unidentified computer, try PC ret ; ;The computer is a PCJR. ; pcjr: mov adapter,2 ;set adapter to PCJR jmp init2 ;jump to install program ; ;The computer is a PC. Check for the presence of an Enhanced Graphics Adapter ;by looking for an 'IBM'signature in the EGA Bios area. ; pc: mov ax,0c000h ;set ES to EGA BIOS segment mov es,ax mov di,1eh ;starting address of signature lea si,ibm_signature ;point si to 'IBM' text mov cx,3 ;three characters to check cld ;clear df repe cmpsb ;compare the three bytes je init2 ;signature found - EGA present ; ;The computer is a PC, but the display adapter is not an EGA. It must be ;either a CGA or an MDA. ; mov adapter,1 ;set ADAPTER for CGA or MDA ; ;Save the current interrupt 1Ch vector and replace it with a new routine. ; init2: mov ah,35h ;DOS function - get vector mov al,1ch ;interrupt 1ch int 21h ;get the vector mov int_1ch_ptr,bx ;save offset of vector mov int_1ch_ptr[2],es ;save segment of vector mov ah,25h ;DOS function - set vector mov al,1ch ;interrupt 1ch lea dx,countdown3 ;point - countdown3 routine int 21h ;set vector ; ;Save the current interrupt 16h vector and replace it with a new routine. ; mov ah,35h ;DOS function - get vector mov al,16h ;interrupt 16h int 21h ;get the vector mov int_16h_ptr,bx ;save offset of vector mov int_16h_ptr[2],es ;save segment of vector mov ah,25h ;DOS function - set vector mov al,16h ;interrupt 16h lea dx,new_int_16h ;pointer to new routine int 21h ;set vector ; ;Set user vector interrupt 4dh to unblank routine. ; mov ah,25h ;DOS function - set vector mov al,4dh ;interrupt 4dh lea dx,unblank ;point to unblank routine int 21h ;set vector mov dx,(offset initialize - seg_org + 15) shr 4 ;... ;prepare DX for exit mov ah,31h ;terminate-but-stay-resident int 21h ;dos function call initialize endp ; code ends end begin