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I have been reading about embedded systems, and particularly the reset modes. As I understand a microcontroller can have several reset modes.

What is brownout reset (BOR) and power on reset (POR)? What is the difference between BOR and POR?

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When the Vdd drops below a brown out threshold voltage, BOR will hold the microcontroller in reset state. Not all devices have BOR detection, but most do, and some have multiple voltage thresholds to select from.
Between a BOR and Power On Reset the whole range of startup voltages can be covered to protect for proper operation after a power drop at the Vdd line.

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  • $\begingroup$ And POR is a reset the embedded device experiences upon power-up. POR voltage is always less than BOR voltage. Below POR, the device typically does nothing. It must reset in order to initialize all of it's features and input/output pins. Often, this reset can also be instantiated from it's running code, to reset itself if needed. On some devices, it may reset itself if an error condition is encountered also (regardless of any power issues.) $\endgroup$ – rdtsc Aug 30 '15 at 3:05

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