I'm designing a prototype that uses the MC9S12XEP100 microcontroller and I'm taking as an example the EVB9S12XEP100 evaluation board. The following questions have arisen.
1) Regarding decoupling capacitors, I used the information present in the datasheet, mainly in the Appendix C PCB Layout Guidelines. Analyzing the EVB9S12XEP100 board, I found that 10uF polarized capacitors are used together with the decoupling capacitors, however, I did not find reference to these 10uF capacitors in the MC9S12XEP100 datasheet.
2) The VDPLL, VDD, VDDF pins have 220nF decoupling capacitors to earth, however. Since the EVB9S12XEP100 evaluation board makes them available externally, I would like to know if there is a need to connect these pins to an external voltage source .
3) Regarding the ocylator circuit, I noticed that, on the EVB9S12XEP100 card, there are two circuits, one of them uses full swing Pierce (FSP) with crystal and the other uses a clock generator. Is there any reason to use the external clock instead of a higher frequency oscillator?
With my best regards,