Hi Bahri,
The link you gave is very informative, which adds to the list of why I hate Microsoft's Software. But cannot help using it because most (all) of my customers are having Windows OS.

I have been using the code developed in VB6.0 which requires the RTS to toggle. I have used the following:
MSComm.RTSEnable=True ; makes RTS High
MSComm.RTSEnable=False ; makes RTS Low.

I have been using the above since many years on various operating systems and found them to be working OK. I had trouble in adjusting the delay between the last byte and RTSEnable=False. Well now it is taken care of and works fine.
Later I we developed an intelligent RS232~RS485 convertor which does not require the RTS pin at all.

Bye,
Mr. Kiran V. Sutar.