The stm32f4 discovery datasheet DS8626 specifies vil and vih as below
So I have some questions based on the documentation
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How do I know that what value VDD is operating at if I use the usb to power the board?
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Why are there two Min or Max values for Vil and Vih? Does that have to do with CMOS vs TTL idea? Which one do I choose?
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Background
I am trying to make a simple circuit where I have a push button and led on a bread board make the led blink with the push button using the pins on the stm32f4. Basically rather than using the push button/led that is available on the board I want to try making the same circuit but just on a breadboard and use the stm32f4 board to process inputs from the push button to get some practice.
So I am confused about how much voltage I need to supply push button vs what the board needs to determine logic levels.
Best Answer
That is actually the datasheet for the controller sitting in the middle of your board. The board itself is documented in UM1472.
Looking at the schematics in the User Manual above, there is this circuit.
According to the relevant datasheets, VOUT of the
LD3985M33Ris 3.3V, the forward voltage drop onBAT60JFILMis 0.3 to 0.4 V at reasonable currents, that gives 2.9 to 3.0 V. But the actual voltage should not matter at all, because you are going to power the switch with the same VDD, or connecting the switch to ground, and pulling up the pin with a resistor to VDD, aren't you?It is explained in the footnotes right below the table.
There is theory and practice, you know...
Just power your button with the 3V pin on the discovery board.