Serial Port Control is an inexpensive royalty-free ActiveX component. You can use it with any ActiveX-enabled development environment, such as VC++, VB, Delphi, etc. Just put it on a form and vou've got all the functionality you need to access an RS232 port. The event driven architecture makes it a snap to use. Just define a function in your program and it will be triggered automatically when new data is available through the port.
