mov CX, 1            ; CX...1    number of bytes to read
    lea DX, znak  ; pointer to read buffer

continues:
    mov AH, 3Fh           ; file read by filehandle
    int 21h               ; INT21 ... file read
    cmp AX,0
    jz  koniec_suboru     ;uz nic neprecitalo - koniec suboru