🚀 go-pugleaf

> The way to enable the TX section of RS485 transceiver is
> drive the RTS signal, so I used the SetCommState API setting
> the fRtsControl field of DCB to RTS_TOGGLE value.

> This approach works fine in any PC I tried from Windows95
> to WinXP.

IMHO, you've only been lucky.

At first, RTS_CONTROL_TOGGLE is not supported under Win95, Win98 
and WinMe as stated in MSDN: 
http://msdn.microsoft.com/library/default.asp?url=/library/en-us/devio/base/dcb_str.asp.

Secondly, as far as I know, there's no way to control the real 
end of transmission under WindowsNT/2000/XP. In the old time of 
DOS, we could read the status of the shift register. That could 
also be done under Win95/98 although not a clean solution. 
Nevertheless, through Windows API, we can check the status 
(empty or not) of the trasmission buffer that is not necessary 
the serial trasmission status (finished or not).

> I have a problem on a DELL notebook with WinXP SP2 and 
> CENTRINO processor.
> My application sends a frame but RTS signal remains high for 
> 15 ms.
> instead of 1-2 ms.!!!!!

That's strange, anyway. RTS goes down sooner than the end of 
transmission, usually. Maybe a particular serial driver is 
installed there.

> I tried to install the trial versione of BDS2006 and recompile 
> my
> project and...suprise...it works well and RTS signal goes down
> in 1 ms.!

I don't know about this.

> Is there someone can explain me this behaviour?

Not the last one. Instead, about how to handle properly a 485 
transmission under WinXP, well, I've been looking for a good 
solution for years... no one found so far.

> How can I work around this bug using C++Builder6?

A good suggestion? Use a "smart" 232/485 converter. No need to 
drive the RTS signal any more.

HTH,

Stefano.