Hi Hennie

>In windows there is no way to detect >that all characters in the buffer were >sent without
>the use of third party device drivers.

I suposse you are using some kind of RS485 to RS232 converter, so the serial port is used and detecting that all the chars has been sent is the same that generate an event when TX buffer become empty. If you are using MSCOMM32.OCX (provided with the Windows OS) you can detect it setting

MsComm.Sthreshold = 1

When the chars in the TX buffer is less than 1, its say 0, the buffer is empty and the comEvSend is generated. With your OnComm Subroutine you can decide what to do when the buffer is empty.

Hope this helps, if you need more info you can contact me directly in order to avoid a long off topic thread.

Best regards.

Fran Dominguez.