Martin Belohorka

115200 on MC9S08QE128 with a high bus and system clock

Discussion created by Martin Belohorka on Dec 17, 2009
Latest reply on Dec 17, 2009 by Tony Papadimitriou



I am developing a system that will need to communicate at 115200 in the temperature span of +20 to +70 celcius. As internal oscillator are known to be temperature dependent, I guess I have to use an external crystal (Correct?). I also need a fairly fast bus clock and system clock.


Right now, during development, I am using the internal oscillator at 36 kHz, trimmed it during programming to 36 kHz. I have a bus clock of ~18 MHz and and a FLL output clock of ~36 MHz.


I can use the same values with an external crystal that matches the internal oscillator. A 36 kHz crystal, but as they are about ten times as expensive as for instance a 3,6864 cyrstal, I wonder if there are any other settings (using a more common crystal) that will allow me to have a relative high system speed and 11520 baud rate.


Best regards