Alex Mogurenko`s Blog

From time to time i have tasks to read/write data to Com port, for example:

1. Sending/Receiving sms (using GSM modem)

2. Working with com port connected printer

3. GPS device

4. Some exotic devices, so on

there tons components you can find using google, but perhaps i was so lazy to find what i need or something else… anyway there werent anything dificult so  i did my own

for that we need 8 WinApi functions:

CreateFile
GetCommState
SetCommState
SetCommTimeouts
EscapeCommFunction
CloseHandle
WriteFile
ReadFile

Opening Port:

function TComPort.Open() : Boolean;
var
PortDCB : TDCB;
Timeouts : COMMTIMEOUTS;
begin
Result := False;
FHandle := CreateFile(PChar(FName),
GENERIC_READ or GENERIC_WRITE,
0, nil, OPEN_EXISTING,
0, 0); //trying to open com port

if (FHandle = INVALID_HANDLE_VALUE) then
exit;//com port was nor oppened for some reasons

FillChar(PortDCB, sizeof(TDCB), #0);
PortDCB.DCBlength := sizeof(TDCB);
GetCommState(FHandle, PortDCB); //getting port state

PortDCB.BaudRate := FBaudRate;
PortDCB.ByteSize := 8;
PortDCB.Parity := NOPARITY;
PortDCB.StopBits := ONESTOPBIT;
PortDCB.Flags := FFlags;//4243;

if (not SetCommState(FHandle, PortDCB)) then
exit;

Timeouts.ReadIntervalTimeout := MAXDWORD;
Timeouts.ReadTotalTimeoutMultiplier := MAXDWORD;
Timeouts.ReadTotalTimeoutConstant := FReadTimeOut; //read timeout
Timeouts.WriteTotalTimeoutMultiplier := MAXDWORD;
Timeouts.WriteTotalTimeoutConstant := FWriteTimeOut; //write timeout

if (not SetCommTimeouts(FHandle, Timeouts)) then
exit;

EscapeCommFunction(FHandle, 11);

Result := True;
end;

Reading from port:

function TComPort.Read() : String;
var
dwRead : Cardinal;
begin
Result := '';
//reading from port
ReadFile(FHandle, m_pBuf^, 1024, dwRead, nil);
Result := String(m_pBuf);
SetLength(Result, dwRead);
end;

Writing to port:

Function TComPort.Write(AData : string) : boolean;
var
m_ppBuf : Pointer;
dwWrote, dwCurWrote : Cardinal;
begin
Result := False;
m_ppBuf := @Pointer(AData)^;
dwWrote := 0;
while (dwWrote < Length(AData)) do

begin
//writing to port
if (not WriteFile(FHandle, Pointer(LongInt(m_ppBuf) + dwWrote)^, length(AData) - dwWrote, dwCurWrote, nil)) then
begin
exit;
end;

Inc(dwWrote, dwCurWrote);
end;

Result := True;
end;

P.S. Download class, sources and example application you can from:

http://alexmogurenko.com/Examples/ComPort.zip

Filed under: Programming