WriteFile Function for I/O 1

[Denyson]

Hi,

I´m trying to use the writefile function to send and receive some datas by serial port (COM 1).

Could anybody tell me how to use correctly the Writefile function for I/O serial communications and also give me an example about how to declare their parameters and how to use the function.

Thanks
Denyson

 

[Guest_imported]

Hi I´m looking for a simple programm to read and write on the serial port under WinNT 4 SP 5
with Microsoft Visual C++ Standart Edition.
Can anybody send me a simple examble programm??

Thank you very much

Jan.Wirl@acts.de

 

[chiph]

The usual trick to using WriteFile with a com port is the call to CreateFile. The trick is you have to use "COM1:"
as the filename (or COM2, etc). I'm not 100% sure about the colon, though. Try it with and without.

Afterwards, you can read and write it just like any other file.

Once you've got basic read/write functionality, you might want to investigate I/O Completion Ports. These will help you handle the case where you try and read from the port when the other end hasn't sent anything (your program blocks).

Chip H.

 

[StukA]

Here's some example code for initializing a serial port. I used this class for simple (no flow control or handshaking) serial communications.

SerialConnection::SerialConnection(string port_name, BaudRate baud, Parity parity, DataBits data_bits, StopBits stop_bits)
{
old_dcb = new DCB; //Pointers for Get/SetCommState
new_dcb = new DCB;
COMMTIMEOUTS timeout;

if (port_name != "COM1" && port_name != "COM2" && port_name != "COM3" && port_name != "COM4" )
throw WBException(WBException::INV_PORT_NAME);

port = CreateFile( port_name.data(),
GENERIC_READ | GENERIC_WRITE,
0,
0,
OPEN_EXISTING,
0,
0);
if (port == INVALID_HANDLE_VALUE)
throw WBException(WBException::SER_PORT_ERR);

GetCommState(port, old_dcb);

*new_dcb = *old_dcb;

new_dcb->BaudRate = (baud ? CBR_9600 : CBR_4800);
new_dcb->ByteSize = (data_bits ? 8 : 7);
new_dcb->fParity = (parity ? EVENPARITY : NOPARITY);
new_dcb->StopBits = (stop_bits ? TWOSTOPBITS : ONESTOPBIT);
new_dcb->fOutxDsrFlow = 0;
new_dcb->fOutxCtsFlow = 0;
new_dcb->fDsrSensitivity = 0;

SetCommState(port, new_dcb);

timeout.ReadIntervalTimeout = 500;
timeout.ReadTotalTimeoutMultiplier = 100;
timeout.ReadTotalTimeoutConstant = 100;

SetCommTimeouts(port, &timeout);
}

And this is the sending function:

int SerialConnection::Send(const char* send_block, int length)
{
DWORD bytes_written;
for (int i = 0; i < length; ++i)
{
WriteFile(port, send_block, 1, &bytes_written, NULL);
send_block++;
if (bytes_written < 1)
throw WBException(WBException::SER_PORT_ERR);
Sleep(100);
}
return bytes_written;
}

 

[chiph]

StukA -

Pretty good looking code!

Can you post it as a FAQ for others to view?

Thanks.
Chip H.

 

[StukA]

Sure - I'll be more than happy to do that. It was no fun figuring this stuff out!

 

[Cagliostro]

StukA, so far I see this question is frequently asqued. I think is a good idea you to write a FAQ. John Fill

ivfmd@mail.md

 

[frankiecifarra]

Great article