STM32U585 Tamp Mechanism

[batuburgu]

Greetings,

I am working on a project involving RTC and TAMP mechanism of U5 series MCUs, specifically STM32U585. I have some questions about the working principle of the TAMP pins. 

In the reference manual RM0456, it is written that the TAMP pins checks if the line is opened or it is shorted (Section 64.1: "Active tamper which increases the security level by auto checking that the tamper pins are not externally
opened or shorted.").

I was able to make the open circuit detection work but I couldn't make the shorting detection work, that might be my fault though. The shorting detection is available in U585 right? 

Also I was wondering how precise is the shorting detection? Let's assume I have a 50 meters long transmission line, can it detect if the line is shorted about 50 centimeters (the line is now 45.5 meters)? If not, how much length of the tranmission line must be removed to make the TAMP pins detect it? In addition, should I do anything to make the shorting detection active or is enabling the active tamper detection enough?

Also, does the TAMP pins have any capability of capacitive or inductive measurement to add an extra layer of protection?

Thanks in advance.

[Gyessine]

>I was able to make the open-circuit detection work, but I could not make the short-circuit detection work. That might be my fault. The short-circuit detection is available in the STM32U585, correct?

Yes, the STM32U5 supports protection against both external open-circuit and short-circuit conditions on the tamper line.
To test the short-circuit case, you don't need to physically shorten the wire, just short the tamper line to GND and verify whether the tamper event is triggered.

>Also, do the TAMP pins have any capability for capacitive or inductive measurement to add an extra layer of protection?

I think you can work something out. you can design an external circuit so that changes in capacitance or inductance influence the voltage or waveform seen by the TAMP pin.
In the end, the capacitance and inductance equations affect the voltage.

If the circuit is designed so that:

• Under normal conditions, the values of capacitance or inductance produce the expected voltage or waveform.
• Any tamper event changes the capacitance or inductance, which then changes the pin voltage or timing beyond the detection threshold.

Then, the TAMP logic may detect the change and trigger the tamper response, such as erasing backup data.

BR
Gyessine

[batuburgu]

Hi, thanks for your answer. 

I need the TAMP pins to understand when the wire is physically shorten, therefore the GND solution doesn't work for me. Is it cabaple of doing so?