unit Unit1;

interface

uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, StdCtrls;

type
  TForm1 = class(TForm)
    ComboBox1: TComboBox;
    procedure FormCreate(Sender: TObject);
    procedure ComboBox1DropDown(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;

var
  Form1: TForm1;

implementation
uses Registry;
{$R *.dfm}

procedure EComPorts(Ports: TStrings);
var
  KeyHandle: HKEY;
  ErrCode, Index: Integer;
  ValueName, Data: string;
  ValueLen, DataLen, ValueType: DWORD;
  TmpPorts: TStringList;
begin
  ErrCode := RegOpenKeyEx(
    HKEY_LOCAL_MACHINE,
    'HARDWARE\DEVICEMAP\SERIALCOMM',
    0,
    KEY_READ,
    KeyHandle);

  if ErrCode <> ERROR_SUCCESS then begin
    // raise EComPort.Create(CError_RegError, ErrCode);
    Ports.Clear;
    Exit;
  end;

  TmpPorts := TStringList.Create;
  try
    Index := 0;
    repeat
      ValueLen := 256;
      DataLen := 256;
      SetLength(ValueName, ValueLen);
      SetLength(Data, DataLen);
      ErrCode := RegEnumValue(
        KeyHandle,
        Index,
        PChar(ValueName),
        Cardinal(ValueLen),
        nil,
        @ValueType,
        PByte(PChar(Data)),
        @DataLen);

      if ErrCode = ERROR_SUCCESS then
      begin
        SetLength(Data, DataLen);
        TmpPorts.Add(Data);
        Inc(Index);
      end;

    until (ErrCode <> ERROR_SUCCESS) ;

    TmpPorts.Sort;
    Ports.Assign(TmpPorts);
  finally
    RegCloseKey(KeyHandle);
    TmpPorts.Free;
  end;

end;

procedure TForm1.FormCreate(Sender: TObject);
begin
//
EComPorts(ComboBox1.Items);
ComboBox1.ItemIndex :=0;
end;

procedure TForm1.ComboBox1DropDown(Sender: TObject);
begin
EComPorts(ComboBox1.Items);
end;

end.