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20.4.4 Power-on-clear reset operation
The supply voltage (V
DD
each hardware unit is initialized to a specific status.
The detection voltage (V
While V
< V
, the system is reset. Reset is released when V
DD
POC
oscillation stabilization time of the main clock oscillator is secured, and then the CPU starts program execution.
Note that, because the main clock oscillator stops during the reset period, the oscillation stabilization time must be
secured. The oscillation stabilization time is determined by the default value of the OSTS register (for the oscillation
stabilization time, refer to 19.2 (3) Oscillation stabilization time selection register (OSTS) and CHAPTER 25
MASK OPTION/OPTION BYTE).
The following table shows the status of each hardware unit during the period of reset effected by the POCRES
signal and after release of reset.
Table 20-4. Hardware Status During Reset Operation by Power-on-Clear
Item
Main clock oscillator (f
)
X
Subclock oscillator (f
)
XT
Internal oscillator (f
)
R
Peripheral clock (f
to f
/1024)
XX
XX
Internal system clock (f
)
CLK
CPU clock (f
)
CPU
Watchdog timer 1 clock (f
)
XW
CPU
Internal RAM
I/O lines (P00)
I/O lines (ports other than P00)
On-chip peripheral I/O registers
Watchdog timer 2
Other on-chip peripheral functions
CHAPTER 20 RESET FUNCTION
) and detection voltage (V
POC
) is 2.6 V ±0.1 V.
POC
During Reset
Oscillation stops
Oscillation continues
Oscillation stops
Operation stops
Operation stops
Operation stops
Operation stops
Initialized
Undefined if power-on reset or writing data to RAM (by CPU) and reset input conflict
(data is damaged).
Otherwise value immediately before reset input is retained.
Low-level output
High impedance
Initialized to specified status
Operation stops
Operation stops
User's Manual U16896EJ2V0UD
) are compared. When V
DD
≥ V
. After release of the reset status, the
DD
POC
Oscillation starts
Oscillation starts
Operation starts after securing oscillation
stabilization time
Operation starts after securing oscillation
stabilization time (initialized to f
Operation starts after securing oscillation
stabilization time (initialized to f
Operation starts
Program execution starts after securing
oscillation stabilization time
Operation starts (f
Operation can be started after securing
oscillation stabilization time
< V
, the system is reset and
POC
After Reset
/8)
XX
/8)
XX
/8)
R
597
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