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I have this assembly code that reads a string of 120 bytes. If I try to fill the buffer by pressing a key until it stops writing, the enter key doesn't work. I counted the characters and I found that I have written 121 characters.

Is this normal? Is there a way to avoid it? Another interruption perhaps?

The code:

.model small
.stack 100h
.386
.data 
    MSG DB "Please give me the string (max 120 chars): ", 10, 13, "$"
    Sentence1 DB 121,?,121 dup(0)
.code
start:
    mov ax, @data
    mov ds, ax

    mov ah,09h
    lea dx,A
    int 21h

    xor ax,ax        
    mov dx, offset Sentence1
    mov ah, 0Ah
    int 21h
    xor bx,bx
    mov bl, Sentence1[1]
    mov Sentence1[bx+2], '$' 

    mov ah, 4ch
    int 21h
end start  

An example (imagine that is a 11 bytes buffer and not 121 bytes, for brevity):

Please give me the string (max 10 chars):
AAAAAAAAAAA
\_________/
     |
    11 As

If I press Enter at this point it doesn't work, but if I delete an A and press Enter, then it works.

I use Tasm and Tlink for compiling.

Regards.

[Edit] A typo.

1

Is this normal?

Yes.

Is there a way to avoid it?

You can use Ctrl+C or Ctrl+Break to exit buffered-input mode (this results in an INT 23h).

Another interruption perhaps?

There are several DOS interrupt services that you could use to read input, but INT 21h/AH=01h is probably the next best option.

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