Are you really sure that the onboard oscillator on your C8051F320 is a crystal controlled frequency. All of the Cygnal / Silicon Labs parts I have looked at the internal oscillator is an R/C type oscillator with a tolerance of about +/-1.5%. You have to take that tolerance into account when computing the actual baud rate going from your microcontroller to the PC serial port.

Silicon Labs has an application note on this subject at their web site. You can either use an external oscillator or real crystal that is spot on the proper serial port frequencies..or you could perform auto-baud detection from some transmit from the PC to the microcontroller. For some idea on auto baud detection you can look here...in my project pages.

Here is the link to the Silicon Labs oscillator information note that I referenced above.

Michael Karas