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GetVidConfig
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;* GetVidConfig - Determines current video configuration and initializes
;* the vconfig structure.
;*
;* Shows: BIOS Interrupt - 10h, Function 0 (Set Video Mode)
;* 10h, Function 0Fh (Get Video Mode)
;* 10h, Function 1Ah (Get or Set Display
;* Combination Code)
;*
;* Uses: vconfig - Video configuration structure, declared in the
;* DEMO.INC include file.
;*
;* Params: None
;*
;* Return: None
GetVidConfig PROC
mov ax, 1A00h ; Request video info for VGA
int 10h ; Get Display Combination Code
chkVGA: cmp al, 1Ah ; Is VGA or MCGA present?
jne chkEGA ; No? Then check for EGA
cmp bl, 2 ; If VGA exists as secondary adapter,
je isCGA ; check for CGA and mono as primary
jb isMONO
cmp bl, 5 ; If EGA is primary, do normal
jbe chkEGA ; EGA checking
chkMCGA:mov vconfig.adapter, MCGA ; Yes? Assume MCGA
mov vconfig.display, COLOR
cmp bl, 8 ; Correct assumption?
ja gmode ; Yes? Continue
isVGA: mov vconfig.adapter, VGA ; Assume it's VGA color
je gmode ; Yes? Continue
mov vconfig.display, MONO ; No? Must be VGA mono
jmp SHORT gmode ; Finished with VGA, so jump
chkEGA: mov ah, 12h ; Call EGA status function
mov bl, 10h
sub cx, cx ; Clear status bits
int 10h ; Get Configuration Information
jcxz chkCGA ; If CX is unchanged, not EGA
isEGA: mov vconfig.adapter, EGA ; Set structure fields for EGA
mov vconfig.display, MONO ; Assume EGA mono
or bh, bh ; Correct assumption?
jnz gmode ; Yes? Continue
mov vconfig.display, COLOR ; No? Must be EGA color
jmp SHORT gmode ; Finished with EGA, so jump
chkCGA: int 11h ; Get equipment list
and al, 30h ; If bits 4-5 set, monochrome
cmp al, 30h ; Monochrome text mode?
je isMONO ; Yes? Continue
isCGA: mov vconfig.adapter, CGA ; No? Must be CGA
mov vconfig.display, COLOR
mov vconfig.CGAvalue, 29h ; Value for CGA 80x25 text,
jmp SHORT gmode ; color, blink enable
isMONO: mov vconfig.adapter, MDA ; Set MONO
mov vconfig.display, MONO
gmode: mov ah, 0Fh
int 10h ; Get Video Mode
mov vconfig.mode, al ; Record mode
mov vconfig.dpage, bh ; and current page
cmp al, 7 ; Monochrome text mode?
je @F ; Yes? Continue
cmp al, 3 ; Color text mode?
je @F ; Yes? Continue
cmp al, 2 ; Black/white 80-col mode?
je @F ; Yes? Continue
mov ax, 0003h ; If not 80-col text mode,
mov vconfig.mode, al ; request Function 0, mode 3
int 10h ; Set Video Mode to 80-col
@@: mov al, vconfig.display ; Multiply display value
cbw ; (which is either 0 or 1)
mov bx, 800h ; by 800h, then add to B000h
mul bx ; for segment address of
add ax, 0B000h ; video buffer
add ah, vconfig.dpage ; Adding display page gives
mov vconfig.sgmnt, ax ; address of current page
mov vconfig.rows, 24 ; Assume bottom row # = 24
cmp vconfig.adapter, EGA ; EGA or VGA?
jl exit ; No? Exit
mov ax, 1130h ; Yes? Request character info
sub bh, bh ; Set BH to valid value
push bp ; BP will change, so save it
int 10h ; Get number of rows/screen
mov vconfig.rows, dl ; Keep in structure
pop bp ; Restore BP
exit: ret
GetVidConfig ENDP
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