| Discovery Zone: Keeping Knowledge Free! |
Another great reference
Assembly Language Programs and Organizations of the IBM PC
|
ASSEMBLY PROGRAMMING AND OS DESIGN
2.
Intro to Assembly
2.1
Data Types
2.2
Registers
2.3
DOS Int Calls
2.4
Basic Commands
2.4.1 DOS Hello World
2.5 BIOS Int Calls
2.5.1
BIOS Hello World
2.6 String Routines
<HOME>
|
Another great reference |
Need a good reference? Assembly Language Step-by-Step: Programming with DOS and Linux, 2nd Edition |
TERM_X db 0
TERM_Y db 0
TEXT_PROPERTY db 1fh
TERM_CURSOR db "_"
CURSOR_MEM dw 0
;====================================
; cls
;====================================
_CLS: push CX
push GS
push BX
mov AX,0b800h
mov GS,AX
mov AL,0
mov AH,[TEXT_PROPERTY]
mov CX,3200
mov BX,0
.LOOP: mov [GS:BX],AX
inc BX
inc BX
dec CX
jnz .LOOP
mov [CURSOR_MEM],AX
pop BX
pop GS
pop CX
ret
;====================================
; putc(ch) where BL contains ch
;====================================
_PUTC: push DX
push ES
push SI
mov AX,0b800h
mov ES,AX ;set up screen segment
mov BH,[TEXT_PROPERTY] ;load display property
mov SI,0 ;screen address
mov AL,160 ;screen is 160 BYTES in width
mul byte [TERM_Y] ;AX=160*TERM_Y
mov DL,[TERM_X] ;DL=TERM_X
movzx DX,[TERM_X] ;DX=DL
shl DX,1 ;DX=DX*2 - 2 BYTES per char
add AX,DX ;AX=AX+DX - offset in screen
add SI,AX
mov AL,[TERM_X] ;AL=TERM_X for updating
cmp BL,13 ;process CR
je CARRIAGE_RETURN
cmp BL,10 ;ignore LF
je DONE2
cmp BL,0
je DRAW_CURSOR
mov [ES:SI],BX
inc SI
inc SI
inc AL
cmp AL,40
jb DRAW_CURSOR
CARRIAGE_RETURN:
mov BX,[CURSOR_MEM] ;replace old cursor with mem
mov [ES:SI],BX
xor AL,AL
inc byte [TERM_Y] ;adjust x and y to next line
cmp byte [TERM_Y],25
jb DRAW_CURSOR
dec byte [TERM_Y]
mov SI,160
mov DI,0
mov CX,24*160
rep
ES movsw
mov CX,160
mov AH,[TEXT_PROPERTY]
mov AL,0
rep
stosw
DRAW_CURSOR: mov [TERM_X],AL ;recompute address for cursor
mov SI,0 ;screen address
mov AL,160 ;screen is 160 BYTES in width
mul byte [TERM_Y] ;AX=160*TERM_Y
mov DL,[TERM_X] ;DL=TERM_X
movzx DX,[TERM_X] ;DX=DL
shl DX,1 ;DX=DX*2 - 2 BYTES per char
add AX,DX ;AX=AX+DX - offset in screen
add SI,AX
DONE1: mov AH,[TEXT_PROPERTY]
mov AL,[TERM_CURSOR]
mov BX,[ES:SI]
mov [CURSOR_MEM],BX
mov [ES:SI],AX
DONE2: pop SI
pop GS
pop DX
ret
;====================================
; puts(string*) - where BX points to
; NULL terminated string
;====================================
_PUTS: push BX
xor AX,AX
mov SI,BX
.LOOP: mov BL,byte [SI]
cmp BL,0
je DONE_PUTS
call _PUTC
inc SI
inc AX
jmp .LOOP
DONE_PUTS: pop BX
ret
;====================================
; puthex(hex) - where BL contains
; value to display in hex
;====================================
_PUTHEX: push BX
push CX
shl BX,4
shr BL,4
cmp BL,10
jb ITS_A_NUMBERL
add BL,7 ;48+17=65 which is ASCII for 'A'
ITS_A_NUMBERL:
add BL,48
mov CL,BL
shr BX,4
shr BL,4
cmp BL,10
jb ITS_A_NUMBERH
add BL,7 ;48+17=65 which is ASCII for 'A'
ITS_A_NUMBERH:
add BL,48
call _PUTC
mov BL,CL
call _PUTC
pop CX
pop BX
ret
;=======================================
; set_term_xy(x,y) - where BH contains y
; coordinate and BL contains x
;=======================================
_SET_TERM_XY: push BX
push DX
push ES
push SI
mov AX,0b800h
mov GS,AX ;set up screen segment
mov SI,0 ;screen address
mov AL,160 ;screen is 160 BYTES in width
mul byte [TERM_Y] ;AX=160*TERM_Y
mov DL,[TERM_X] ;DL=TERM_X
movzx DX,[TERM_X] ;DX=DL
shl DX,1 ;DX=DX*2 - 2 BYTES per char
add AX,DX ;AX=AX+DX - offset in screen
add SI,AX
mov AX,[CURSOR_MEM]
mov [ES:SI],AX
mov [TERM_X],BX
mov BH,[TEXT_PROPERTY] ;load display property
mov SI,0 ;screen address
mov AL,160 ;screen is 160 BYTES in width
mul byte [TERM_Y] ;AX=160*TERM_Y
mov DL,[TERM_X] ;DL=TERM_X
movzx DX,[TERM_X] ;DX=DL
shl DX,1 ;DX=DX*2 - 2 BYTES per char
add AX,DX ;AX=AX+DX - offset in screen
add SI,AX
mov AX,[ES:SI]
mov [CURSOR_MEM],AX
mov BL,[TERM_CURSOR]
mov [ES:SI],BX
pop SI
pop ES
pop DX
pop BX
ret
;====================================
; set_text_property(pr) - where BL
; contains pr
;====================================
_SET_TEXT_PROPERTY:
mov [TEXT_PROPERTY],BL
ret