Автор: http://www.swissdelphicenter.ch

function TestPrinterStatus(LPTPort: Word): Byte;
var
  Status: byte;
  CheckLPT: word;
begin
  Status := 0;
  if (LPTPort >= 1) and (LPTPort <= 3) then
  begin
    CheckLPT := LPTPort - 1;
    asm
      mov dx, CheckLPT;
      mov al, 0;
      mov ah, 2;
      int 17h;
      mov &Status, ah;
    end;
  end;
  Result := Status;
end;

{
  Pass in the LPT port number you want to check & get the following back:
  01h - Timeout
  08h - I/O Error
  10h - Printer selected
  20h - Out of paper
  40h - Printer acknowledgement
  80h - Printer not busy (0 if busy)

  Note:
  This function doesn't work under NT, it gives an access violation
  from the DOS interrupt call.
 }