;**********************************************************************************************
;*                                                                                            *
;*              LAB3-6.ASM - Assembler Laboratory ZMiTAC                                      *
;*                                                                                            *
;*    program that displays characters from the file on the screen                            *
;*                                                                                            *
;**********************************************************************************************

comment %
*********************************************
* display bytes from the text file          *
*********************************************
%

.model small

.stack 512

.data
file      db "disp.txt", 0
character db ?
handle    dw ?

.code
start:
        mov ax, seg file
        mov ds, ax
        ; open input file
        mov dx, offset file      ; DS:DX - ASCIIZ of filename
        mov ah, 3Dh              ; open file
        mov al, 0                ; open for reading
        int 21h                  ; call DOS function
        jc open_error            ; CF set -> error
        mov handle, ax           ; file handle

copy_loop:
        ; read character
        mov dx, offset character ; buffer address
        mov bx, handle           ; file handle
        mov cx, sizeof character ; buffer size
        mov ah, 3Fh              ; read data
        int 21h
        jc close_file            ; jump on read error
        cmp ax, 0
        jz close_file            ; nothing to display
        ; display character
        mov ah, 02h
        mov dl, character
        int 21h                  ; write character

        jmp copy_loop

close_file:
        mov ah, 3Eh              ; close input file
        mov bx, handle
        int 21h

open_error:
        mov ax, 4C00h            ; exit
	int 21h
end start