MSP430 MCU reset

There are two reset signals for MSP430: power-on reset signal (POR) and power-on clear signal (PUC). There are also signals that can trigger POR and PUC: 5 from the watchdog, 1 from the reset pin, and 1 from the signal generated by an error in writing the FLASH key value.

The POR signal occurs only in two situations: (1) the microprocessor is powered on; (2) the system is reset when a low level is generated on the RST/NMI pin.

The conditions for the generation of the PUC signal are as follows: (1) the POR signal is generated; (2) the watchdog timer overflows when the watchdog is valid; (3) an error occurs when writing the watchdog timer security key value; (4) an error occurs when writing the FLASH memory security key value.

The relationship between POR and PUC: The generation of POR signal will cause the system to reset and generate PUC signal. However, PUC signal will not cause the generation of POR signal.

Whether it is a reset triggered by a POR signal or a PUC signal, the MSP430 will read the reset interrupt vector from address 0xFFFE, and the program will start executing from the address pointed to by the interrupt vector. Among the conditions for triggering the PUC signal, in addition to the POR generating a triggering PUC signal, the other conditions can determine the cause of the PUC signal by reading the corresponding interrupt vector so as to make corresponding processing.

The status after system reset (POR) is as follows: (1) RST/NMI pin function is set to reset function; (2) All I/O pins are set to input; (3) Peripheral modules are initialized, and their register values ​​are the default values ​​in the relevant manual; (4) Status register SR is reset; (5) Watchdog is activated and enters working mode; (6) Program counter PC is loaded with the address at 0xFFFE, and the microprocessor starts executing the program from this address.