
iiiPeriPheraLModuLes1(systeM):CLoCkManageMentunit(CMu)
iii-1-4
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iii.1.2.4Precautionstobetakenduringinitialreset
CoreCPu
When initially reset, all internal registers of the core CPU (except PSR) become unstable. Therefore, these
registers must be initialized in a program. In particular, the Stack Pointer (SP) should always be initialized
before accessing the stack. Note that NMI requests are masked in hardware until data is written to the SP after
initial reset, to prevent erratic operation.
internalraM
The content of internal RAM becomes unstable when initially reset. Internal RAM must be initialized as
required.
high-speed(osC3)oscillatorcircuit
When initially reset, the high-speed (OSC3) oscillator circuit starts oscillating, and when the reset signal is
deasserted, the CPU starts operating with the OSC3 clock. To prevent erratic operation due to an instable clock
when the chip is reset at power-on or while the high-speed (OSC3) oscillator circuit is idle, the reset signal
should not be deasserted until after oscillation stabilizes.
Low-speed(osC1)oscillatorcircuit
When the chip is reset at power-on or while the low-speed (OSC1) oscillator circuit is idle, the low-speed
(OSC1) oscillator circuit also starts oscillating. The low-speed (OSC1) oscillator circuit requires a longer time
for oscillation to stabilize than the high-speed (OSC3) oscillator circuit. (See the electrical characteristics
table.) To prevent erratic operation due to an instable clock, the OSC1 clock should not be used until after this
stabilization time elapses.
input/outputportsandinput/outputpins
Initial reset initializes the control and data registers of the input/output ports, therefore, be set up back again in
a program.
otherinternalperipheralcircuits
The control and data registers of other peripheral circuits are initialized or made unstable by initial reset.
Therefore, these registers should be set up as required in a program.
For details on how peripheral circuits are initialized by initial reset, see each I/O map or circuit description.