|Interface||Max voltage||Microcontroller pin||Assigned IC||Resistor|
|UART_3||3.3 V||37||IC1||Series resistor|
|RS232_1||3.3 V||15||IC8||Series resistor|
|RS232_2||3.3 V||23||IC6||Series resistor|
|IC only||5 V||80||IC2||Series resistor|
The pull-downs has a weak 100 k Ohm pull-down pin, while the series resistor pins have a 1 k Ohm series resistor and a 1.37 k Ohm pull-down resistor. This will be likely be changed to a voltage divider in newer versions.
Absolute maximal ratings
The voltage on any 3.3 V pin should be within -0.3 V and (VDD + 0.3 V) with respect to VSS, where VDD should be 3.3 V.
The voltage on any 5 V pin should be within -0.3 V and (5.5 V) with respect to VSS.
Input low voltage is registered as lower than: 0.2 * VDD = 0.66 V for I/O pins.
Input high voltage is registered as higher than: 0.8 * VDD = 2.64 V for I/O pins.