We have serial port software that drivers plotters for the last 15+ years that has used the Windows API function TransmitCommChar(). Many of out users have been upgrading their computers which not come with no serial ports so they are reverting to USB to Serial cable solutions. These solutions worked under XP and Vista 32 bit systems, but they do not work under Windows 7 x64. If the app makes the TransmitCommChar() call the system will transmit the character but never return to the application. I'm in communications with number of chip manufacturers but things are moving to slow. has anyone else seen this problem? If so, what are you doing. We do not want people using PCI cards only from the stand point that we are not sure they are capable of installing one properly or that they have laptops.