My information is coming from here. The assignment asks for a program that reads in no more than 20 characters, converts those characters to upper case, and then prints the input as capitals.
I have no idea how to access the input from int21/AH=0ah. I really can't ask a more precise question unless I understand what is linked above. Can someone explain? Also, I'm using TASM if that makes any difference. Also, I'm testing this on freedos.
UPDATE1:
Alright, thanks to your help, I believe I understand how the interrupt needs to be set up and behaves.
Setup:
I have to designate a ds:dx where I want this buffer to exist
I have to set ds:dx to 20 (which sets the max number of characters the buffer can hold)
I have to set ds:dx+1 to 0 (which I think somehow set a min number of characters to read in)
Actually call int21/AH=0ah, which will go to ds:dx and interpret the preset bytes. It will halt the program while it waits for input
int21/AH=0ah will fill from ds:dx+2+n with my input (where n is the number of characters input including '\r')
My question is now, how do I do this. I've just looked through the x86 Assembly Language Reference again, but haven't been able to find anything helpful yet.
Code I've got so far
assume cs:code,ds:code
code segment
start:
mov ax,code ;moves code segment into reg AX
mov ds,ax ;makes ds point to code segment
mov ah,0ah
int 21h
mov ax,1234h ;breakpoint
mov ah,9
mov dx,offset message
int 21h
endNow:
;;;;;;;;;;ends program;;;;;;;;;;
mov ah,0 ;terminate program
int 21h ;program ends
message db 'Hello world!!!',13,10,'$'
code ends
end start
That DOS function retrieves a buffer with user input. See this table. It seems that program is using that call to pause execution waiting for the user to resume the program.
Edit: I just reread the question. I thought you were only asking what the function call did in your given source. If you want to read input of no more than 20 characters, you first need memory to store it. Add something like this:
bufferSize db 21 ; 20 char + RETURN
inputLength db 0 ; number of read characters
buffer db 21 DUP(0) ; actual buffer
Then fill the buffer:
mov ax, cs
mov ds, ax ; ensure cs == ds
mov dx, offset bufferSize ; load our pointer to the beginning of the structure
mov ah, 0Ah ; GetLine function
int 21h
How to convert to uppercase is left to the reader.
That description says you put the address of a buffer in ds:dx before calling the interrupt. The interrupt will then fill that buffer with the characters it reads.
Before calling the interrupt, the first byte of the buffer is how many characters the buffer can hold, or 20 in your case. I do not understand the description of the second byte of the buffer (on input to the interrupt), so I would set it to zero. On return, that byte will tell you how many characters of input were read and placed into the buffer.
.model small
.stack 100h
.data
N db ?
msg db 10,13,09,"Enter number of arrays---->$"
.code
.startup
mov ax,@data
mov ds,ax
call read_N;read N from console
mov ah,4ch
int 21h
Read_N proc
;get number of arrays from user
push ax
push dx
readAgain:
mov ax,03h ;Clear screen
int 10h
mov dx,offset msg
mov ah,09h
int 21h
call ReadNumber
;Inuput number must be in 2<=N<=10 bounery
cmp al,2
js readAgain ;input out of boundary read again
cmp al,10
jg readAgain
mov N,al
pop dx
pop ax
ret
Read_N endp
ReadNumber proc
;read decimal number 0-99 using
;character by character in askii and conver in to decimal
;return result in al
xor ax,ax
xor bx,bx
xor dx,dx
mov ah,01h
int 21h
sub al,'0' ;conver in to decimal
mov bl,al
mov ah,01h
int 21h
cmp al,0dh ;Exit if enter pressed
jnz cont
mov al,bl
jmp exit
cont:
sub al,'0' ;conver in to decimal
mov dl,al
xor al,al
xor bh,bh
mov cx,bx
addnum:
add al,10
loop addnum
add al,dl
exit:
ret
ReadNumber endp
end
