There are several considerations when choosing the specific device in the family. In particular, the number of pins in the package determines certain connectivity of the supply voltages. Some packages have a separate VIO supply pin that allows the connection of different logic levels to the MCU. In other cases, the package does not have a VIO pin external and the IO voltage should be treated as though it were connected to VDD. Another aspect to consider is the VPP voltage. If the system is going to take advantage of in-system programming, then a 4.7µF capacitor is required on the VPP pin. This is used to provide the programming voltage to the MCU and it is not recommended to attach any other components to this pin. If the system will not use the IAP feature, then the pin can be used as general purpose I/O.

