hi,



Which API do you mean? We use 9-bit communication via _outp() and _inp(). COM port initialization looks like:

#define PORT	0x3F8
//...
	_outp(PORT+3, (128+32+8+2+1));		// 8 bit, 1 stop, parity always 1
	_outp(PORT+1, 0);			// baudrate
	_outp(PORT+0, 1);			//	115200
	_outp(PORT+3, (32+8+2+1));		// 8 bit, 1 stop, parity always 1  
//...

Our protocol uses syncronization bytes with 9th bit = 1 and data bytes with 9th bit = 0. To send it we use:

// send sync byte to COM port with 9th bit = 1
void SendSyncByte (unsigned char sync)
{
	while (! (_inp(PORT+5) & 32))
	{}					// wait till port ready
	_outp(PORT+3, (32+8+2+1));		// 8 bit, 1 stop, parity always 1
	_outp(PORT+0, sync);
}
// send data byte to COM port with 9th bit = 0
void SendDataByte (unsigned char data)
{
	while (! (_inp(PORT+5) & 32))
	{}					// wait till port ready
	_outp(PORT+3, (32+16+8+2+1));		// 8 bit, 1 stop, parity always 0
	_outp(PORT+0, data);
}

To receive and determine data/sync we use next:

// read from COM port
unsigned int ReadByte (unsigned int time_out)
{
	unsigned int data, timeout = time_out;
	unsigned char status;

	_outp(PORT+3, (32+8+2+1));		// 8 bit, 1 stop, parity always 1
	while (! ((status = _inp(PORT+5)) & 1))
	{
		if (! timeout--)
			return (0xFFFF);	// timeout
	}
	data = (unsigned int)_inp(PORT+0);
	if (status & 8)	return (0xFFFE);	// frame error
	if (!(status & 4)) data += 256;		// determine sync/data;
//						return data as 0...255
//						and sync as 256...511
	return (data);
}

This works at least for Win98. The only one restriction is that it is not possible to send/receive bytes simultaneously because parity control is modifyed depend on send/read. So only half-duplex mode used: PC sends to MCU sync+data then MCU answers with sync+data.

Regards,
Oleg