F²MC-16FX Family, Hardware Set Up
Document No. 002-04772 Rev. *B
10
4
Port Input / Unused Pins / Latch-up
How to connect Input Port Pins and how to proceed with unused Pins
4.1
Port Input / Unused Pins
It is strongly recommended to do not pins unconnected, while they are switched to input. In this case those pins can
enter a so-called
floating state
. This can cause a high I
CC
current, which is adverse to low power modes. Also
damage of the MCU can happen.
Use the internal pull-up resistors in this case. If not, use external pull-up or pull-down resistors to define the input-
level.
The recommended
way is to set the port input enable to “0”, if a port pin is unconnected.
Never connect a potential divider with almost same resistor values.
Be careful with connection of input pins to other devices, which can go into High-Z states. Always use internal pull-up
or external pull-up or pull-down resistors in this case.
Outputs from external circuits should always be connected via a serial resistor to a MCU input pin to prevent latch-up
effects caused by under- or overshoots (4.2).
Debouncing and decoupling capacitors should always be chosen as smallest as possible. Please refer to chapter 4.2
All pins are set to input disabled after its power-on default.
Do not connect any input ports directly to VCC or VSS (GND)! Always use pull up or down resistors (2k … 4k
Ohms).