I have 3 devices on the same serial port and my protocol uses 9-bit serial with the 9th bit indicating address or data.  Unfortunately the PC serial port is unable to do 9-bit mode but I found that setting the parity to either mark or space works as a suitable replacement.  The issue is I need to be able to switch parity modes and would like to switch fast to send many data packets per Processing frame (each device is driving RGB LED's and my Processing script uses Minim to analyze the audio stream and flash the lights accordingly).