November 17, 2017

The STM32F103C8T6 and GPIO

Voltages and levels

Some of the GPIO pins are dubbed as "5 volt tolerant". Not as many as you might think or hope though. See the markings on the diagram below.
Or if that is too convenient for you, look at the tables in the "Pinouts and Pin Description" chapter (chapter 3) of the datasheet, and look for "FT" in the "IO level" column.

What "5V tolerant" means is that there are clamping diodes to 3.3 volts (or whatever the processor is running on) and the port will not be destroyed by 5 volt inputs. Apparently it is even possible to connect them to an i2c device running on 5 volts and have things work. You need to disable the pullups in this scenario. No telling about the uarts, but it is hopeful. The structure of a port looks like what is in the diagram before (but I don't think this applies to a port in analog input mode).

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