9.3 Functional Description
9.3.1 Device Reset
Upon entering a reset state from any source, the following events occur:
• The processor core halts program execution.
• Special Function Registers (SFRs) are initialized to their defined reset values.
• External port pins are placed in a known state.
• Interrupts and timers are disabled.
SFRs are reset to the predefined reset values noted in the detailed register descriptions. The contents of internal data memory are
unaffected during a reset; any previously stored data is preserved. However, since the stack pointer SFR is reset, the stack is effective-
ly lost, even though the data on the stack is not altered.
The port I/O latches are reset to 0xFF (all logic ones) in open-drain mode. Weak pullups are enabled during and after the reset. For
Supply Monitor and power-on resets, the RSTb pin is driven low until the device exits the reset state.
Note:
During a power-on event, there may be a short delay before the POR circuitry fires and the RSTb pin is driven low. During that
time, the RSTb pin will be weakly pulled to the supply pin.
On exit from the reset state, the program counter (PC) is reset, the watchdog timer is enabled, and the system clock defaults to an
internal oscillator. Program execution begins at location 0x0000.
EFM8UB3 Reference Manual
Reset Sources and Power Supply Monitor
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