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System Reset and Initialization
2-2 System Resets, Interrupts, and Operating Modes
2.1 System Reset and Initialization
The system reset circuitry shown in Figure 2−1 sources both a power-on reset
(POR) and a power-up clear (PUC) signal. Different events trigger these reset
signals and different initial conditions exist depending on which signal was
generated.
Figure 2−1. Power-On Reset and Power-Up Clear Schematic
POR
Latch
S
R
PUC
Latch
S
R
Resetwd1
Resetwd2
S
S
Delay
RST/NMI
WDTNMI
†
WDTSSEL
†
WDTQn
†
WDTIFG
†
EQU
†
MCLK
POR
PUC
S
(from flash module)
KEYV
SVS_POR
0 V
V
CC
0 V
Brownout
Reset
† From watchdog timer peripheral module
~ 50us
A POR is a device reset. A POR is only generated by the following three
events:
- Powering up the device
- A low signal on the RST/NMI pin when configured in the reset mode
- An SVS low condition when PORON = 1.
A PUC is always generated when a POR is generated, but a POR is not
generated by a PUC. The following events trigger a PUC:
- A POR signal
- Watchdog timer expiration when in watchdog mode only
- Watchdog timer security key violation
- A Flash memory security key violation