INTRODUCTION The following example is a simple program to read a file and print the contents to a standard printer. It gets the filename of the file to print from the DOS command prompt input line. The prompt input information is passed to the program in a buffer area of the Program Segment Prefix (PSP). The address of the Program Segment Prefix is passed to the program in the ES and DS registers when the program execution starts. This program checks the keyboard between every character printed for an escape key code to terminate execution of the program. ; This program prints a file defined on the command line.MODEL small;************* Stack Section *********************.STACK 500;************* Data Section **********************.DATApsp_seg dw 0no_cl_mess db "This routine requires that a " db "filename be on the command line for printing." db 0dh,0ah,"Please try with a filename.",0dh,0ah,"$"file_bad_open db "Bad file open",0dh,0ah,"$"file_bad_read db "Bad file read",0dh,0ah,"$"printer_bad_mess db "!! Printer Error !!!!",0dh,0ah,"$"printing_mess db "A file is being printed,",0dh,0ah db "To stop printing, Press ESC key",0dh,0ah,"$"filename db 128 dup(0)file_handle dw 0file_count dw 0file_pointer dw offset file_bufferfile_buffer db 1024 dup(0); ************* ----------- *********************;************* Code Section *******************.CODEstart proc near ;DS and ES are indexing PSP area mov al,[DS:80H] ;load AL with size of data line mov dx,@data ;get segment address of data area mov ds,dx ;point DS to data area mov psp_seg,ES ;save PSP address cmp al,1 ;?? data in DOS command line ?? ja get_PSP_filename ;branch if data found ;if here, there is no data on command line ;display error message to user and terminate lea dx,no_cl_mess;-------------------------terminate_display: ;display message indexed by DX then terminate mov ah,09 int 21H ;DOS Call;-------------------------terminate_program:;terminating the program mov ah,4CH ;set AH for terminating function mov al,00 ;set terminating code variable int 21H ;call DOS to terminate;------------------------------------------; %%%%%%%%%%%%% ----------- %%%%%%%%%%%%%%%get_PSP_filename: ;move PSP filename to filename buffer in our data area mov ax,ds mov es,ax ;point ES to data segment mov ds,psp_seg mov si,82H ;SI source is PSP data area lea di,filename cld ;make strings go forward get_PSP_data_1: lodsb ;load string data byte ;check for end of filename cmp al,21H ;branch if end of string jb got_PSP_filename stosb ;store string data byte jmp get_PSP_data_1got_PSP_filename: mov al,0 stosb ;make ASCIIZ string with zero end push es pop ds ;reset data segment pointer;try to open file mov ah,3dH lea dx,filename mov al,0 ;read access code int 21H ;DOS Call jnc file_open_ok lea dx,file_bad_open jmp terminate_display;+++++++++++++++++++++++++++++++++++++++++++;############### +++++++++++ ###############file_open_ok: ;save file handle mov file_handle,ax lea dx,printing_mess ;display start message mov ah,09 int 21H ;DOS Callfile_read: ;read in block of file data mov ah,3fH lea dx,file_buffer mov cx,1024 mov bx,file_handle int 21H ;DOS Call jnc file_read_ok ;branch if good read ;else read file error occurred ;close file mov ah,3eh mov bx,file_handle int 21H ;index exit error message lea dx,file_bad_read jmp terminate_displayfile_read_ok: ;check to see if no more file data cmp ax,0 je close_file ;branch if no data left ;else reset data block size and pointer mov file_count,ax lea bx,file_buffer mov file_pointer,bx;!!!!!!!!!!!!!!!!! ^^^^^^^^ !!!!!!!!!!!!!!!!!!!!print_data_block: ;main loop to print block of file data ;scan keyboard to check for any keys mov ah,1 int 16H jz print_data_block_1 ;branch if no key ;get key code out of buffer mov ah,0 int 16H ;call BIOS keyboard cmp al,01BH ;check key code je close_file ;branch if ESCprint_data_block_1: mov si,file_pointer mov al,[si] mov ah,0 mov dx,0 ;select LPT1 int 17H ;BIOS Call test ah,25H jnz printer_error inc si mov file_pointer,si dec file_count jnz print_data_block ;loop if more data ;else go read in next block of file data jmp file_read;!!!!!!!!!!!!!!!! ^^^^^^^^ !!!!!!!!!!!!!!!!!!!!close_file: mov ah,3eh mov bx,file_handle int 21H ;DOS Call jmp terminate_program;-------------- ?????????? -------------------printer_error: ;index exit error message lea dx,printer_bad_mess jmp terminate_display;_______________________________________________start endp ;end of start procedure end start ;define start as beginning of program
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