🚀 go-pugleaf

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Hi assembler users,

Assembler is power! Borland's compilers are fantastic!

Here I attached a program that clears the screen in text mode.
It can be used without parameters to clear screen through INT 10h or
with parameter /M or /m clearing the screen using direct access to video
memory. Last method is much faster.

CLRSCR.ASM should be compiled and linked with Borland Turbo Assembler.
tasm /ml clrscr.asm
tlink clrscr.obj /t
/t - gernerate .COM file

The function 0Ah of INT 21h is called "Buffered Keyboard Input" and is used
as follows:

 AH = 0A
 DS:DX = pointer to input buffer of the format:

  max | count  |  BUFFER (N bytes)
                            BUFFER is the input buffer
             count is the number of characters returned (byte)
    max is the maximum number of characters to read (byte)

 returns nothing

 - since strings can be pre-loaded, it is recommended that the
   default string be terminated with a CR
 - N bytes of data are read from STDIN into buffer+2
 - max buffer size is 255, minimum buffer size is 1 byte
 - chars up to and including a CR are placed into the buffer
   beginning at byte 2; Byte 1 returns the number of chars
   placed into the buffer  (extended codes take 2 characters)
 - DOS editing keys are active during this call
 - INT 23 is called if Ctrl-Break or Ctrl-C detected



Best wishes,
Jesus

tunney wrote:

> I know that this is a thick question, but could someone explain to me
> how to clear the screen in text and video mode, can't for the life of me
> figure out how. Please help me I have an exam in this soon.
> Also could someone explain int 21h service 0Ah
>
> Thanks a million.



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.model TINY
.code
org 100h

;----------------- Program Entry point --------------------------
Entry:
	jmp	Init		; go to initialization

;--- switch stack and set memory allocation


useMem		db	0


include video.inc



Start:

	call	videoInit
	or	al, al				; use memory? (AX is preserved in videoInt)
	jne	Use_Mem

	mov	bh, 07h				; gray chars on black background
	xor	ax, ax
	mov	cx, ax				; upper row and column (0,0)
	mov	dl, video_Cols
	mov	dh, video_Rows
	call	videoCpag
	jmp	Finish

Use_Mem:
	call	clearScrMem

Finish:
	mov	ah, 4Ch
	int	21h



Init:
	xor	ax, ax
	mov	si, 80h				; command tail
	lodsb					; get the length
	or	al, al				; check if none
	jz	Init_X
	mov	cl, al
	sub	ch, ch				; put count in cx

;--- loop through characters in command tail

Init_C:
	lodsb					; load next byte	
	cmp	al, '/'				; check if switch
        je      Init_F				; jump if so
Init_L:
	loop	Init_C				; otherwise loop back

Init_X:
	jmp	Start

;--- found slash

Init_F:
	dec	cx				; reduce count	
	jz	Init_X				; jump if no more bytes

	lodsb					; load command character	
	sub	al, 'a'-'A'			; convert to upper-case
	cmp	al, 'M'				; check if M
	jne	Init_N
	inc	ah

Init_N:
	xchg	al, ah
	jmp	Start

	mov	ax, 4cffh			; exit function
	int	21h				; execute

END Entry

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video_Mode	db	?	; present mode
video_Page	db	?	; active page
video_Seg	dw	0B800h	; video segment (for direct memory access), color by default
video_Cols	db	?	; screen columns
video_Rows	db	?	; screen rows
video_Size	dw	?	; video page size in bytes

MONO		equ	7	; monochrome video mode


videoInt	proc	near
	push	di
	push	si
	push	bp
	int	10h			; call video
	pop	bp
	pop	si
	pop	di
	ret
endp	; videoInt


videoInit	proc	near

	push	es
	push	ax
	push	bx

	mov	ah, 0Fh			; function
	call	videoInt		; interrupt 10H
	mov	video_Mode, al		; save mode
	dec	ah			; screen columns 0-79, not in 1-80 format
	mov	video_Cols, ah		; save columns
	mov	video_Page, bh		; save page

	mov	ax, 0040h
	mov	es, ax
	mov	ax, es:[004Ch]		; size of one video page in current mode (4096)
	shr	ax, 10
	mov	bx, 03E8h		; 1000
	imul	bx
	mov	video_Size, ax		; we get exact 4000

	mov	al, es:[0084h]		; rows on the screen -1 (0-24, not 1-25)
	mov	video_Rows, al

	mov	ax, video_Seg
	cmp	video_Mode, MONO
	jne	vInit_X
	mov	ax, 0B000h
	mov	video_Seg, ax

vInit_X:	
	pop	bx
	pop	ax
	pop	es
	ret
endp		; videoInit







;================================================
; Scroll a portion of the screen up.
;
; In: DH= upper left hand row; DL= upper left
; hand column; CH= lower left hand row; cl= lower
; left hand column; AL= lines to scroll (0 means
; clear instead of scroll); BL= attribute to use.
;=================================================
;
video_Spag	proc	near
	push	ax
	mov	ah, 6			; function
	call	videoInt		; interrupt 10H
	pop	ax
	ret
endp		; video_Spag



;================================================
; Clear a portion of the screen.
;
; In: DH= upper left hand row; DL= upper left
; hand column; CH= lower left hand row; cl= lower
; left hand column; BL= attribute to use.
;================================================
;
videoCpag	proc	near
	push	ax
	sub	al, al			; scroll lines zero (blank window)
	call	video_Spag		; clear screen
	pop	ax
	ret
endp		; video_Cpag



clearScrMem	proc	near

	mov	ax, video_Seg
	mov	es, ax
	xor	di, di
	mov	cx, video_Size
	shr	cx, 1
	mov	ax, 0720h
	rep	stosw

	ret
endp		; clearScrMem
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