I'm a new user to this chip and want to use it's serial USART for communicating with an external device. I wish to use the internal oscillator as a clock source so that I can use the external clock pins for I/O. I have found that the stability of the internal clock is 2% which should be adequate for serial comms at 19200 baud. What steps do I have to go through to ensure that the internal clock is set correctly. I must admit to being confused by the trim thing. I have always used an external crystal for previous designs but need a couple of extra pins. Does the default internal clock get set to 32kHz? or is this frequency dependant on the trim register?