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Saturday, August 11, 2012

HOW TO ACCESS PORTS


In the old days of DOS and 16bit Windows, writing to ports (serial, printer, game, video and other ports) in your computer was easy; all you had to do was use the "port[]" command. 
 
Delphi no longer supports the "port[]" command, so you may have to use assembly functions as follows:
 
function ReadPortB
         ( wPort : Word ) : Byte;
begin
  asm
    mov dx, wPort
    in al, dx
    mov result, al
  end;
end;

procedure WritePortB
         ( wPort : Word; bValue : Byte );
begin
  asm
    mov dx, wPort
    mov al, bValue
    out dx, al
  end;
end;
Listing #1 : Delphi code. Download port (0.26 KB).
 
    NOTE:Some operating systems, such as Windows NT, may not let you access ports directly as demonstrated above. In this case, you may have to depend on a third party library to gain proper access to internal ports.
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