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STM32F103VC: gpio protection diodes not working?

Question asked by almar on Feb 11, 2015
Latest reply on Feb 11, 2015 by almar
Hi everybody,
I have a GPIO configured as input pull up. The input conditioning circuit is really simple, it is just an external pull up wich is connected to ground when external event 
occurs.
See attachment for schematic of input circuit.
I want to check if the gpio protection diodes work (the gpio is 5 V tolerant), so by means of a power supply I apply to point A an increasing voltage (current limited to 10 mA) starting from ground. I then monitor the voltage in point B. What I expect is that as voltage applied to A increases the voltage on B increases as well, but it should clamp at some point (around 5 V) regardless the voltage applied to A.
But, this is not the case, if I apply 8 V to A, I read about 8 B also on B.
So, am I missing something? From the STM32F103 reference manual (section 9.1) it seems that the protection diodes are placed soon after the gpio pin so the clamp of protection diodes should be observable  in B.
Thank you for your help!

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