//{$DEFINE COMM_UNIT}

//Простой пример работы с последовательными портами
//Код содержит интуитивно понятные комментарии и строки на шведском языке,
//нецелесообразные для перевода.
//Compiler maakt Simple_Comm.Dll of Simple_Com.Dcu afhankelijk van 1e Regel
(COMM_UNIT)

{$IFNDEF COMM_UNIT}
library Simple_Comm;
{$ELSE}
unit Simple_Comm;
interface
{$ENDIF}

uses Windows, Messages;

const
  M_BaudRate = 1;
const
  M_ByteSize = 2;
const
  M_Parity = 4;
const
  M_Stopbits = 8;

{$IFNDEF COMM_UNIT}
{$R Script2.Res} //versie informatie
{$ENDIF}

{$IFDEF COMM_UNIT}
function Simple_Comm_Info: PChar; StdCall;
function
  Simple_Comm_Open(Port: PChar; BaudRate: DWORD; ByteSize, Parity, StopBits:
    Byte; Mas
  k: Integer; WndHandle: HWND; WndCommand: UINT; var Id: Integer): Integer;
    StdCall;
function Simple_Comm_Close(Id: Integer): Integer; StdCall;
function
  Simple_Comm_Write(Id: Integer; Buffer: PChar; Count: DWORD): Integer; StdCall;
function Simple_Comm_PortCount: DWORD; StdCall;

const
  M_None = 0;
const
  M_All = 15;

implementation
{$ENDIF}

const
  InfoString = 'Simple_Comm.Dll (c) by E.L. Lagerburg 1997';
const
  MaxPorts = 5;

const
  bDoRun: array[0..MaxPorts - 1] of boolean
  = (False, False, False, False, False);
const
  hCommPort: array[0..MaxPorts - 1] of Integer = (0, 0, 0, 0, 0);
const
  hThread: array[0..MaxPorts - 1] of Integer = (0, 0, 0, 0, 0);
const
  dwThread: array[0..MaxPorts - 1] of Integer = (0, 0, 0, 0, 0);
const
  hWndHandle: array[0..MaxPorts - 1] of Hwnd = (0, 0, 0, 0, 0);
const
  hWndCommand: array[0..MaxPorts - 1] of UINT = (0, 0, 0, 0, 0);
const
  PortCount: Integer = 0;

function Simple_Comm_Info: PChar; stdcall;
begin

  Result := InfoString;
end;

//Thread functie voor lezen compoort

function Simple_Comm_Read(Param: Pointer): Longint; stdcall;
var
  Count: Integer;

  id: Integer;
  ReadBuffer: array[0..127] of byte;
begin

  Id := Integer(Param);
  while bDoRun[id] do
  begin
    ReadFile(hCommPort[id], ReadBuffer, 1, Count, nil);
    if (Count > 0) then
    begin
      if ((hWndHandle[id] <> 0) and
        (hWndCommand[id] > WM_USER)) then

        SendMessage(hWndHandle[id], hWndCommand[id], Count,
          LPARAM(@ReadBuffer));

    end;
  end;
  Result := 0;
end;

//Export functie voor sluiten compoort

function Simple_Comm_Close(Id: Integer): Integer; stdcall;
begin

  if (ID < 0) or (id > MaxPorts - 1) or (not bDoRun[Id]) then
  begin
    Result := ERROR_INVALID_FUNCTION;
    Exit;
  end;
  bDoRun[Id] := False;
  Dec(PortCount);
  FlushFileBuffers(hCommPort[Id]);
  if not
    PurgeComm(hCommPort[Id], PURGE_TXABORT + PURGE_RXABORT + PURGE_TXCLEAR +
      PURGE_RXCL
    EAR) then

  begin
    Result := GetLastError;
    Exit;
  end;
  if WaitForSingleObject(hThread[Id], 10000) = WAIT_TIMEOUT then
    if not TerminateThread(hThread[Id], 1) then
    begin
      Result := GetLastError;
      Exit;
    end;

  CloseHandle(hThread[Id]);
  hWndHandle[Id] := 0;
  hWndCommand[Id] := 0;
  if not CloseHandle(hCommPort[Id]) then
  begin
    Result := GetLastError;
    Exit;
  end;
  hCommPort[Id] := 0;
  Result := NO_ERROR;
end;

procedure Simple_Comm_CloseAll; stdcall;
var
  Teller: Integer;
begin

  for Teller := 0 to MaxPorts - 1 do
  begin
    if bDoRun[Teller] then
      Simple_Comm_Close(Teller);
  end;
end;

function GetFirstFreeId: Integer; stdcall;
var
  Teller: Integer;
begin

  for Teller := 0 to MaxPorts - 1 do
  begin
    if not bDoRun[Teller] then
    begin
      Result := Teller;
      Exit;
    end;
  end;
  Result := -1;
end;

//Export functie voor openen compoort

function
  Simple_Comm_Open(Port: PChar; BaudRate: DWORD; ByteSize, Parity, StopBits:
    Byte; Mas
  k: Integer; WndHandle: HWND; WndCommand: UINT; var Id: Integer): Integer;
    stdcall;

var
  PrevId: Integer;
  ctmoCommPort: TCOMMTIMEOUTS; //Lees specificaties voor de compoort
  dcbCommPort: TDCB;
begin

  if (PortCount >= MaxPorts) or (PortCount < 0) then
  begin
    result := error_invalid_function;
    exit;
  end;
  result := 0;
  previd := id;
  id := getfirstfreeid;
  if id = -1 then
  begin
    id := previd;
    result := error_invalid_function;
    exit;
  end;
  hcommport[id] := createfile(port, generic_read or
    generic_write, 0, nil, open_existing, file_attribute_normal, 0);

  if hcommport[id] = invalid_handle_value then
  begin
    bdorun[id] := false;
    id := previd;
    result := getlasterror;
    exit;
  end;
  //lees specificaties voor het comm bestand
  ctmocommport.readintervaltimeout := maxdword;
  ctmocommport.readtotaltimeoutmultiplier := maxdword;
  ctmocommport.readtotaltimeoutconstant := maxdword;
  ctmocommport.writetotaltimeoutmultiplier := 0;
  ctmocommport.writetotaltimeoutconstant := 0;
  //instellen specificaties voor het comm bestand
  if not setcommtimeouts(hcommport[id], ctmocommport) then
  begin
    bdorun[id] := false;
    closehandle(hcommport[id]);
    id := previd;
    result := getlasterror;
    exit;
  end;
  //instellen communicatie
  dcbcommport.dcblength := sizeof(tdcb);
  if not getcommstate(hcommport[id], dcbcommport) then
  begin
    bdorun[id] := false;
    closehandle(hcommport[id]);
    id := previd;
    result := getlasterror;
    exit;
  end;
  if (mask and m_baudrate <> 0) then
    dcbCommPort.BaudRate := BaudRate;
  if (Mask and M_ByteSize <> 0) then
    dcbCommPort.ByteSize := ByteSize;
  if (Mask and M_Parity <> 0) then
    dcbCommPort.Parity := Parity;
  if (Mask and M_Stopbits <> 0) then
    dcbCommPort.StopBits := StopBits;
  if not SetCommState(hCommPort[Id], dcbCommPort) then
  begin
    bDoRun[Id] := FALSE;
    CloseHandle(hCommPort[Id]);
    Id := PrevId;
    Result := GetLastError;
    Exit;
  end;
  //Thread voor lezen compoort
  bDoRun[Id] := TRUE;

  hThread[Id] := CreateThread(nil, 0, @Simple_Comm_Read, Pointer(Id), 0,
    dwThread[Id]
    );

  if hThread[Id] = 0 then
  begin
    bDoRun[Id] := FALSE;
    CloseHandle(hCommPort[Id]);
    Id := PrevId;
    Result := GetLastError;
    Exit;
  end
  else
  begin
    SetThreadPriority(hThread[Id], THREAD_PRIORITY_HIGHEST);
    hWndHandle[Id] := WndHandle;
    hWndCommand[Id] := WndCommand;
    Inc(PortCount);
    Result := NO_ERROR;
  end;
end;

//Export functie voor schrijven naar compoort;

function
  Simple_Comm_Write(Id: Integer; Buffer: PChar; Count: DWORD): Integer; stdcall;
var
  Written: DWORD;
begin

  if (Id < 0) or (id > Maxports - 1) or (not bDoRun[Id]) then
  begin
    Result := ERROR_INVALID_FUNCTION;
    Exit;
  end;
  if not WriteFile(hCommPort[Id], Buffer, Count, Written, nil) then
  begin
    Result := GetLastError();
    Exit;
  end;
  if (Count <> Written) then
    Result := ERROR_WRITE_FAULT
  else
    Result := NO_ERROR;
end;

//Aantal geopende poorten voor aanroepende applicatie

function Simple_Comm_PortCount: DWORD; stdcall;
begin

  Result := PortCount;
end;

{$IFNDEF COMM_UNIT}
exports

  Simple_Comm_Info Index 1,
  Simple_Comm_Open Index 2,
  Simple_Comm_Close Index 3,
  Simple_Comm_Write Index 4,
  Simple_Comm_PortCount index 5;

procedure DLLMain(dwReason: DWORD);
begin

  if dwReason = DLL_PROCESS_DETACH then
    Simple_Comm_CloseAll;
end;

begin

  DLLProc := @DLLMain;
  DLLMain(DLL_PROCESS_ATTACH); //geen nut in dit geval
end.

{$ELSE}
initialization
finalization

  Simple_Comm_CloseAll;
end.
{$ENDIF}

Другое решение: создание модуля I / O(ввода / вывода)под Windows 95 / NT.Вот он:
  )

(с TDCB в SetCommStatus вы можете управлять DTR и т.д.)
(Примечание: XonLim и XoffLim не должны быть больше 600, иначе под NT это
  работает неправильно)

unit My_IO;

interface

function OpenComm(InQueue, OutQueue, Baud: LongInt): Boolean;
function SetCommTiming: Boolean;
function SetCommBuffer(InQueue, OutQueue: LongInt): Boolean;
function SetCommStatus(Baud: Integer): Boolean;
function SendCommStr(S: string): Integer;
function ReadCommStr(var S: string): Integer;
procedure CloseComm;

var

  ComPort: Word;

implementation

uses Windows, SysUtils;

const

  CPort: array[1..4] of string = ('COM1', 'COM2', 'COM3', 'COM4');

var

  Com: THandle = 0;

function OpenComm(InQueue, OutQueue, Baud: LongInt): Boolean;
begin

  if Com > 0 then
    CloseComm;
  Com := CreateFile(PChar(CPort[ComPort]),
    GENERIC_READ or GENERIC_WRITE,
    0, nil, OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL, 0);
  Result := (Com > 0) and SetCommTiming and
    SetCommBuffer(InQueue, OutQueue) and
    SetCommStatus(Baud);
end;

function SetCommTiming: Boolean;
var

  Timeouts: TCommTimeOuts;

begin

  with TimeOuts do
  begin
    ReadIntervalTimeout := 1;
    ReadTotalTimeoutMultiplier := 0;
    ReadTotalTimeoutConstant := 1;
    WriteTotalTimeoutMultiplier := 2;
    WriteTotalTimeoutConstant := 2;
  end;
  Result := SetCommTimeouts(Com, Timeouts);
end;

function SetCommBuffer(InQueue, OutQueue: LongInt): Boolean;
begin

  Result := SetupComm(Com, InQueue, OutQueue);
end;

function SetCommStatus(Baud: Integer): Boolean;
var

  DCB: TDCB;

begin

  with DCB do
  begin
    DCBlength := SizeOf(Tdcb);
    BaudRate := Baud;
    Flags := 12305;
    wReserved := 0;
    XonLim := 600;
    XoffLim := 150;
    ByteSize := 8;
    Parity := 0;
    StopBits := 0;
    XonChar := #17;
    XoffChar := #19;
    ErrorChar := #0;
    EofChar := #0;
    EvtChar := #0;
    wReserved1 := 65;
  end;
  Result := SetCommState(Com, DCB);
end;

function SendCommStr(S: string): Integer;
var

  TempArray: array[1..255] of Byte;
  Count, TX_Count: Integer;

begin

  for Count := 1 to Length(S) do
    TempArray[Count] := Ord(S[Count]);
  WriteFile(Com, TempArray, Length(S), TX_Count, nil);
  Result := TX_Count;
end;

function ReadCommStr(var S: string): Integer;
var

  TempArray: array[1..255] of Byte;
  Count, RX_Count: Integer;

begin

  S := '';
  ReadFile(Com, TempArray, 255, RX_Count, nil);
  for Count := 1 to RX_Count do
    S := S + Chr(TempArray[Count]);
  Result := RX_Count;
end;

procedure CloseComm;
begin

  CloseHandle(Com);
  Com := -1;
end;

end.