GPIOs Electrical specs

There is an absolute maximum current of 40 mA on the GPIOs. This is the current beyond which things will be expected to let out the magic smoke. The GPIO documents indicate that the buffer strength is 20 mA, that would be, the current sourced or sunk before the voltage is pulled out of the range indicated by the Voh or Vol specs. Since this range is 0.2V we can estimate the resistor in the Thevenin equivalent circuit of the output as being 10 Ω. In other words, all IO lines when driven as outputs have their High Vio or Low 0V with a 10 Ω resistance in series.

Maximum input voltageVi max 3.6 V.
Input current HighIih 10 μA
Input current LowIil -10 μA
Tri-state output currentIoz 10 μA
Pull-up resistanceRpu 100 kΩ
Pull-down resistanceRpd 100 kΩ
Output current HighIoh 20 mA
Output current LowIol -20 mA

The GPIO ports operate at different voltages. For the most part, this is noticeable when trying to source voltage to some load -- ports in the PG and PL series have Voh between 1.6 and 1.8 V so feeding this to LEDs will not work well. All ports have Vol close to 0V, so sinking current thru a load returned to the +3.3V line will always work, as all ports tolerate the 3.3V level just fine. Indeed, this is how the "System LED" is wired to the port PL7. (GPIO359, Pin 2 on the Expansion connector) There is a space available for this LED on the board.

Ports PB PC PF PH series

IO voltageVio3.3V
Output Low voltage Vol 0 V 0.2 V.
Output High voltage Voh 3.1 V 3.3 V.
Input Low voltage Vil -0.3 V 0.99 V
Input High voltage Vih 2.31 V 3.6 V

Ports PD PE series

IO voltageVio2.5V
Output Low voltage Vol 0 V 0.2 V.
Output High voltage Voh 2.3 V 2.5 V.
Input Low voltage Vil -0.3 V 0.75 V
Input High voltage Vih 1.75 V 2.8 V

Ports PG PL series

IO voltageVio1.8V
Output Low voltage Vol 0 V 0.2 V.
Output High voltage Voh 1.6 V 1.8 V.
Input Low voltage Vil -0.3 V 0.54 V
Input High voltage Vih 1.26 V 2.1 V

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