Rob:
The problem with using the internal timer for baud rate generation is this.

1) On some parts the internal timer is relatively slow. At least this is true on the F2xx series parts. There is a trade off in providing a clocking function. Cygnal simply decided that those applications where the internal clcoking was interesting should be low power thus low frequency.

2) The internal clock is not nearly precise enough to be used for a reliable baud rate source. It may work at room temp for one part. But change temp or go to a different and then the selected divisor may not be accurate enough.

Thus if you want good baud rates just commit your self to a low cost crystal and two small caps to equip your board with an accurate clocking. I did an F226 design with a 4.9152 MHz crystal and was able to achieve all normal baud rates with ease.

Note I suspect that the internal oscillator on board Cygnal parts is NOT put there primarly for use as the clock in most applications. Rather I suspect that the ocillator is there so that the part will come up running out of reset with only power and ground attached to the processor. This permits the JTAG port to function even of the other types of clock sources are not functional. This way the debug hardware is WAY MORE USEFUL when bringing up a new design or untested board layout.

Michael Karas