Using a GPIO as INPUT
GPIO pins, when used as inputs, can be tied to a digital output of another device and
report its status, provided the device interface levels are compatible with the GPIO 1.8V
CMOS levels.
If a digital output of a device is tied to GPIO input, the pin has interface levels different
than 1.8V CMOS. It can be buffered with an open collector transistor with a 47K ohm pull-
up resistor to 1.8V.
Using a GPIO as OUTPUT
GPIO pins, when used as output, can drive 1.8V CMOS digital devices or compatible
hardware. When set as outputs, the pins have a push-pull output, and therefore the pull-
up resistor can be omitted.
Figure 18: GPIO Output Pin Equivalent Circuit
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